Using Substitution to solve or check
algebraic equations

**Note**: Always use the order of operations to **solve**, **evaluate** or
**compute** any mathematical equation

Here is an example of an algebraic equation where you have
already determined the value of x, y, and z – How should you evaluate it?

*x* = 15, *y* = 6 and
*z* = 4.5

*y*^{2}
– 2*x* + *x* – 3(*z*)

·
Step
1 – Rewrite the entire equation and plug the values in, remember you must put
multiplication signs where needed – see where they have been added below:

6^{2} – 2 ∙ 15 + 15 – 3 ∙ 4.5

·
Step
2 – Solve according to the order of operations

36 – 2 ∙ 15 + 15 – 3 ∙ 4.5

36 – 30 + 15 – 3
∙ 4.5

36 – 30 + 15 – 13.5

6 + 15 –
13.5

21 – 13.5

7.5

Suppose you have an algebraic equation that you wish to
solve and check; here is an example:
Solve for *x*

4*x* =
322

·
Step
1 – solve for *x*

__4__x =
__322__

4
4

*x*
= 8.5

·
Step
2 – Check your solution. Are you
correct?

Substitute
your variable into the equation and check that your equation is balanced (equal
on both sides of the equal sign)

4 ∙
8.5 = 322

322 =
322

Yes it is correct!