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Proofs

Proof means sufficient evidence to establish the truth of something. It is obtained from deductive reasoning, rather than from empirical arguments. Proof must show that a statement is true in all cases, without a single exception.

1,294 Questions

In a parallelogram are the diagonals equal?

No, the properties of a paralleogram are as follows:

  • two parallel sides
  • bisecting diagonals
  • equal opposite angles
  • and it does not need to have all equal sides it just needs to have OPPOSITE equal sides

If the diagonals were equal, the figure would have to be a square, rectangle, or rhombus.

No. In fact they are equal only in exceptional circumstances.

Do a parallelograms diagonals bisect each other?

I can't offer a full proof, but I can suggest some possibilities that will lead you to your proof. In a parallelogram, you can easily demonstrate that the angles formed by a cord extending between parallel lines and the parallel lines themselves, and that are formed on opposite sides of the cord, are equal. This will work for both pairs of triangles in the parallelogram, and can be applied to all of the angles at the corners of the parallelogram. This will lead you to demonstrating that the pairs of triangles "pointing" to each other (not adjacent pairs) are similar, and in fact congruent. From there it is not difficult to establish that the connected sections of the two interior cords are equal.

Do axioms need a proof in the logical system?

An axiom is a statement that is accepted without proof. Proofs are based on statements that are already established, so therefore without axioms we would have no starting point.

Why any number with zero power is equal to 1?

Let a be any number and n any positive integer, an/an = 1 since since anything divided by itself is 1. But the laws of exponents say that an/an =an-n=a0 So this proves that a0 =1

What is the de Morgan's first theorem?

DeMorgan's Theorems are:

1. ~(A&B) ~A&~B.

For example:

"It's not raining and cold" means the same as "It is either not raining, or it is not cold", and

"It's not either raining or cold" means the same as "It's not raining and it's not cold".

Applied recursively, DeMorgan's theorem means that to find the inverse of a complex sentence, change all atoms to their inverses, and change all ANDs to ORs and ORs to ANDs.

Why does multiplying negative integers by negative integers result in positive integers?

Any negative integer can be factored to -1 times its positive value. Because negative one times itself is positive one, when multiplied by each other they cancel out.

So if you're multiplying a negative integer A by a negative integer B. Replace A and B with -1*|A| and -1*|B| (You can do this because you know A and B are negative), and use the distributive property to rearrange them. Now you can see the -1*-1 term and equate it to 1, leaving only the |A| and |B| behind. Because two positive numbers multiplied together are always positive, the result will always be positive.

Represented algebraically, as long as A and B are negative integers, the following is true:

AB = -1|A|*-1|B| = -1*-1|AB| = |AB|.

What is least to greatest?

You have to put them over a common denominator.

These numbers can be expressed as:

66/90 35/90 54/90 50/90

So in order they are:

35/90 50/90 54/90 66/90

Or back in their original terms:

7/18 9/9 3/5 11/15

[Alternatively you could convert them all to decimals.]

What is difference in axiom and postulate?

Theorem: A Proven Statement.

Postulate: An Accepted Statement without Proof.

They mean similar things. A postulate is an unproven statement that is considered to be true; however a theorem is simply a statement that may be true or false, but only considered to be true if it has been proven.

How do you prove lines are parallel in similar triangles?

Given:In a triangle ABC in which EF BC

To prove that:AE/EB=AF/FC

Construction:Draw EX perpendicular AC and FY perpendicular AB

Proof:taking the ratios of area of triangle AEF and EBF and second pair of ratio of area of triangle AEF and ECF.

We get AE/EB and AF/FC

we know that triangle lie b/w sme and same base is equal in area

therefore area of EBF I equal to area of ECF

therefore AE/EB=AF/FC

HENCE PROVED

Should i be 5'4 at 11?

It's very normal...it just means you might not grow very much when you are older...you will grow a little...just not to much more

UPDATE

From personal experience, I was five feet tall at age 11 and I grew to an average height of 5'11". Its different with everyone, but I wouldn't worry about it too much. You'll grow when your body is ready.

Prove or disprove square root of 2 divided by 6 is rational?

let x= square root 6 + square root 30, I will write S(6) for square root 6, or S(n) for square root n x-S(6)=S(30) now square both sides x^2-2S(6)+6=30 or x^2-24=2S(6) Now square both sides again to get rid of the radical sign x^4-48x+24^2=24 or after we simplify x^4-48x-552=0 Now we know x is a solution of this polynomial because we created the polynomial to make it so! But the rational roots theorem tells us that all the solutions can be written as p/q where p is an integer factor of 552 and q is an integer factor of 1 ( it is 1or -1) So the solution must be a factor of 552 if the solution is rational. ( there are irrational and complex solutions) 2^3x3x23=552 so the only possible rational roots are combinations of these factors, but we know square root of 5 +square root of 30 is <8, we could say <10 and also by approximation. So that means we only have to deal with the factors 2,3,4 and 6 (all the other combinations are >or= 8) But we also know sqrt6+sqrt(30)>2,3 or 4 because sqrt 4+sqrt 4=4 and our sum is greater. So we are left with 6 Well we know our sum can be written as Sqrt(6)[(Sqrt5)+ 1)] which tells us it is not 6. So it is none of the possible rational roots and hence not rational. Lots of ways to do this last part, just show that it can't be any of the rational factors. following the above notation, If S(6) + S(30) were rational, then it's square would be rational as well so we will show that 6 + 2S(180) + 30 is not rational it suffices to show that S(180) is irrational becasue addition is closed in the rational numbers. 180 = 36 times 5 so S(180) = 6S(5). Now we simply need to show that S(5) is irrational. Assume that (a/b)^2 = 5 where a/b is a fraction in Lowest Terms. then a^2 = 5b^2 so a^2 is divisible by 5 which means that a is divisible by 5 (see footnote). for some number k, a=5k. now we have 25k^2=5b^2 dividing through by 5 we see that b is also divisible by five, contradicting the fact that a/b was in lowest terms. Q.E.D. *every integer has a unique prime facotization. If the prime factorization of a is P1 * P2 * P3 * ... * Pn and 5 is not included, then squaring a simply squares all the prime factors, and 5, wich is prime will still not be part of the prime factorization.

What is the fraction for pi in circumference?

the fraction 22/7 is often used as an approximation for the value of pi. it is off from the actual value by about 0.04 percent (1 in 2500).

This would be like measuring a football field and being off by about 1.5 inches on your measurement.

The fraction 355/113 is amazingly close, better than 1 part in 10 million

How do you find compound interest?

The formula for compound interest is:

A = P * ( 1 + ( R / N ) )^( N * T )

where

A = amount of money accumulated after n years, including interest.

P = principal amount (the initial amount you borrow or deposit)

R = annual rate of interest (as a decimal)

N = number of times the interest is compounded per year

T = number of years the amount is deposited or borrowed for.

Example:

"John Doe invests $100 in an account earning interest at a rate 4% every 6 months. Calculate the value of his investment a the end of 4 years." ...

A = amount of money accumulated after n years, including interest.

P = 100

R = 4 / 100 = 0.04

N = 2

T = 4

so...

A = P * ( 1 + ( R / N ) )^( N * T )

A = 100 * ( 1 + ( 0.04 / 2 ) )^( 2 * 4 )

A = 100 * 1.02^8

A = 100 * 1.171659381

A = 117.17

So the answer is $117.17
Compound interest formula is A = P (1 + r/n)nt. P is principal, r is annual rate of interest, t stands for number of years, A is the amount, including interest, that accumulates over x amount of years, and n is the number of compounding per year.

The formula for the volume of a sphere?

2 pi r times the circumference sqaured. then take this and find out its square root.

This however, only works if you have the circumference.

If you have both the volume and the height, you can find the formula for the radius by solving the following literal equation for "r":

V=1/3 r^2(3.14)(H)

r=(3V/pi H)square root

What is the definition of interval?

An interval is the distance between two notes.

Example: The interval between C and C-sharp is a half step.

The interval between C and D is a whole step!

Another Times T2 crossword answer to 14d... entre'acte

How many zeros are there in billion?

There are two correct answers to this question:

15 (in the USA and in any countries that use "short scale" naming conventions)

Or

24 (in countries that use "long scale" naming conventions)

To work out the number of zeros from the scales:

  • Long scale
This is based on powers of a million (106) so multiply the name prefix by 6

billion: bi implies 2 → 2 x 6 = 12 zeros

trillion: tri implies 3 → 3 x 6 = 18 zeros

quadrillion: quad implies 4 → 4 x 6 = 24 zeros

quintillion: quin implies 5 → 5 x 6 = 30 zeros

etc

  • Short scale
This is based on powers of a thousand (103) plus one, so multiply 3 by the name prefix plus one.

billion: bi implies 2 → 3 x (2 + 1) = 3 x 3 = 9 zeros

trillion: tri implies 3 → 3 x (3 + 1) = 3 x 4 = 12 zeros

quadrillion: quad implies 4 → 3 x (4 + 1) = 3 x 5 = 15 zeros

quintillion: quin implies 5 → 3 x (5 + 1) = 3 x 6 = 18 zeros

etc

→ quadrillion: quad implies 4 → 3 x (4 + 1) = 3 x 5 = 15 zeros.

What is the process of finding the solution of an equation?

A system of equations simply means, what number can you plug in for X and Y that will make both equations work?

For example,

Solve the following system of equations:

x + y = 11

3x - y = 5

In order to solve a system of equations, you have 2 ways.

Method 1: Substitution

Choose 1 equation. It doesn't matter which!

To make it easier, pick an equation without alot of numbers multiplied to X or Y.

ie: x + y = 11.

Now, solve for X or Y. You pick! OK, I'll pick. (but it doesn't matter which. just pick either!)

I'll solve for X.

x + y = 11

Subtract y from both sides, because I want my equation to look like x = something.

x = 11 - y

Now that we've solved for a variable (x), plug what x is equal to (11-y) into the equation you didn't solve, wherever you see x. Make sure to use parenthesis!

3x - 5 = y

3(11-y) - 5 = y

Now use your algebra to simplify the equation.

33 - 3y -5 = y (distributive property -- this is why we use parenthesis....)

28 - 3y = y

28 = 4y

7 = y

Now that we have a number for Y, plug 7 in wherever you see Y into one of your original equations. We're trying to solve for X now. In fact, to make it easier, you can plug y = 7 into the equation we solved x for!

Remember, x = 11-y ?

x = 11 - (7)

x = 4

So we know y = 7 and x = 4. These numbers should work in BOTH original equations!! If they don't, you made a mistake and you should double check your algebra.

x + y = 11

(4) + (7) = 11

11 = 11 (check)

3x - y = 5

3(4) - (7) = 5

12 - 7 = 5

5 = 5 (check)

Method 2: Elimination

As this method suggests, we need to "eliminate" or get rid of 1 variable.

Line both equations up so the x's and y's are stacked on top of each other, and the = signs as well. Like you were going to do an addition, or subtraction problem.

x + y = 11

3x - y = 5

-------------

What our goal is, is to eliminate one variable. Just like in method 1, you choose which variable. The easiest way is to pick a variable with no numbers in front.

Those y's look pretty good!

When using the elimination method we want 2 things to happen.

1) The number in front of the variable being eliminated is the same in both equations

2) The variable being eliminated must have opposite signs in both equations.

Luckily, our y variable has no coefficient (number in front) AND already has an opposite sign! (+y on top, -y on bottom). All we need to do now is add downward, like a regular addition problem.

1x + 1y = 11

3x - 1y = 5

-----------------

4x = 16

Notice the y's cancelled each other out? They "eliminated" themselves, which was our goal! Remember to add the numbers on the other side of the equals sign as well.

Now just solve for X.

4x = 16 -> x = 4

Once we find a value for x, substitute x=4 into either original equations, to solve for y.

x + y = 11

(4) + y = 11

y = 11 - 4

y = 7

So x =4 and y=7, just like in the first method. Use whichever makes you feel comfortable. I find substitution is much easier, but you might prefer elimination. Good luck!

How do you work out the perimeter of a rectangle?

Take the length of the rectangle and multiply it by the width.

For example, if I had a rectangle with two sides 4 inches in length and two sides 3 inches in length, then the area would be 4x3, which equals 12 square inches.

What is the maximum number of distinct edges in an undirected graph with N vertices?

Let G be a complete graph with n vertices. Consider the case where n=2. With only 2 vertices it is clear that there will only be one edge. Now add one more vertex to get n = 3. We must now add edges between the two old vertices and the new one for a total of 3 vertices. We see that adding a vertex to a graph with n vertices gives us n more edges. We get the following sequence

Edges on a graph with n vertices: 0+1+2+3+4+5+...+n-1. Adding this to itself and dividing by two yields the following formula for the number of edges on a complete graph with n vertices: n(n-1)/2.

Why is the square root of three an irrational number?

I'm assuming that you mean 'square root'. Yes, this sum is irrational. So are each of the two numbers alone. A simple proof can be done by writing x=square root 2 + square root 3 and then "squareing away" the square roots and then use the rational roots theorem. The sum or difference of two irrational number need not be irrational! Look at sqrt(2)- sqrt(2)=0 which is rational.

How can you decide if the difference of two numbers is positive negative or zero without actually calculation the difference?

WHOEVER ANSWERED THIS PREVIOUSLY HAS NO IDEA WHAT WE ARE ALL TALKIN ABOUT , OBVIOUSLY

* * * * *

Ok, here is someone who might know.

If the first number is bigger than the second, the difference is positive;

If the first number is the same as the second, the difference is zero; and

If the first number is smaller than the second, the difference is negative.

How many digits of pi have been found?

Chuck Norris counted to infinity -twice!

Only Chuck Norris can divide by ZERO!

The term "digit" is from the Latin digitus meaning "finger or toe". Therefore there is no such thing as a three digit number, even in pi. And I like pi better than cake. Mmhh...pi!

Is the converse of a true conditional statement always false?

No. Consider the statement "If I'm alive, then I'm not dead." That statement is true. The converse is "If I'm not dead, then I'm alive.", which is also true.

Can the product of two mixed numbers be a whole number?

It's always a common multiple; it's not always least.

Simple counter example:

4 × 6 = 24

But LCM(4, 6) = 12

------------------------------------------------------------------------------------

Note: HCF(4, 6) = 2

What is true of any two whole numbers that the product of the two numbers is equal to the product of their highest common factor and lowest common multiple.

eg 4 × 6 = hcf(4, 6) × lcm(4, 6) = 2 × 12 = 24.