## Answer

###### Wiki User

###### 04/25/2013

If you have:**x****-****2**And you know that **x=6**
...... then you can "substitute" **6** for
**x**:**6****-****2****=****4**

*Example 1:* If x=5 then what is **10/x + 4** ?

Put "5" where "x" is:

10/5 + 4 = 2 + 4 = 6

*Example 2:* If x=3 and y=4, then what is **x2 + xy**
?

Put "3" where "x" is, and "4" where "y" is:

32 + 3×4 = 3×3 + 12 = 21

*Example 3:* If x=3 (but you don't know "y"), then what is
**x2 + xy** ?

Put "3" where "x" is:

32 + 3y = 9 + 3y

(that is as far as you can get)

As that last example showed, you may not always get a number for an answer, sometimes just a simpler formula.

## Negative Numbers

When substituting negative numbers, put () around them so you get the calculations right.*Example 4:* If x = **-2**, then what is **1-x+x2**
?

Put "(-2)" where "x" is:

**1 -** **(-2)** **+** **(-2)****2** = 1 + 2 + 4
= 7

Note: if you don't know why

- the
**- (-2)**became**+2**or - the
**(-2)2**became**+4**

then here is a quick summary: RuleAdding or
SubtractingMultiplying or DividingTwo like signs become a
**positive sign**3+(+2) = 3 **+** 2 = 53 × 2 = 66-(-3) = 6
**+** 3 = 9(-3) × (-2) = 6Two unlike signs become a **negative
sign**7+(-2) = 7 **-** 2 = 53 × (-2) = -6 (-3) × 2 = -68-(+2)
= 8 **-** 2 = 6