Math and Arithmetic

# What is -5c plus 9 and how?

###### Wiki User

###### 2011-01-15 02:18:07

You can't tell a thing about -5c+9 until you know what 'c'

is.

And every time 'c' changes, -5c+9 changes.

## Related Questions

###### Asked in Math and Arithmetic, Units of Measure, Temperature

### At what temperature will Fahrenheit be equal to centigrade?

The correct answer
is of course -40 degrees.
Whilst the equations are both linear, if you were to plot them both
on the same graph, you would see that the results do intersect (at
-40degrees).
Another, slightly more geeky, way to get the answer is to use
the 2 equations
1. F=9/5C +32 ... used to convert from centigrade (Celsius) to
Fahrenheit
2. C= 5/9(F- 32).... used to convert from Fahrenheit to
Centigrade (Celsius)
Firstly write the write the equations so that they are equal
(C=F), and then we can solve the simultaneous equations. So it
looks like this:
9/5C+32 = 5/9(F-32). (this is when Fahrenheit and Celsius/
Centigrade are equal)
Then you solve for either F or C, by substituting for either F
or C into the equation above (1. if you are solving for F, or 2. if
you are solving for C) lets use number 1 and solve for F
It now looks like this:
9/5C+32 = 5/9((9/5C+32)-32) (I just put in (9/5C + 32), where F
used to be.
To solve it we just use some simple rules of equations to try to
get C on its own
Firstly divide both sides by 5/9) and it look like this:
9(9/5C+32)/5 = ((9/5C+32)-32)
Then simplify right hand side by removing the brackets like
this:
9(9/5C+32)/5 = 9/5C [of course 32-32=0]
Next simplify the left hand side by opening brackets (it is done
by multiplying everything inside the brackets by 9):
(81/5C+288)/5 = 9/5C
To get rid of 5 on bottom of left hand side, you muliply both
sides by 5 and get:
(81/5C+288) = 45/5C
Next remove the brackets arent needed (nothing to do outside the
brackets):
81/5C+288 = 45/5C
Next move Cs together and numbers to other side (by taking 288
from both sides and taking 45/5C from both sides), and it looks
like this:
81/5C-45/5C =-288
Now solve the left hand side (easy as they are both over 5C), so
its just 81-45:
36/5C=-288
Next multiply both sides by 5 (gets rid of the 5 on the bottom
of left hand side) and you get:
36C=-1440
Now we divide both sides by 36 (makes C= to 1), and we get:
C=-1440/36
Now whack that into a calculator and Hey Presto:
C=-40
(it also work if you substitute for C)
So the temperature at which Celsius = Fahrenheit is -40
degrees
(I hope this helped)
Use this equation to convert degrees Celsius/Centigrade (ºC) to
degrees Fahrenheit (ºF): [°F] = [°C] × 1.8 + 32