Exercise 4 Page 388

We will solve the equation by isolating x on one side. We can use the Subtraction Property of Equality to subtract 3 from both sides of the equation. This will eliminate the addition and isolate x. Let's do it!

x+3 = 12

SubEqn

LHS-3=RHS-3

x+3 - 3 = 12 - 3

No, see solution.

x=12-3

SubTerms

Subtract terms

x=9

Now we want to check our answer and make sure our solution is correct. Let's substitute x=9 into the original equation and simplify.

x+3 = 12

Substitute

x= 9

9+3? =12

AddTerms

Add terms

12=12 ✓

Since the left-hand side and right-hand side are equal, x=9 is the correct solution.

Extra

Properties of Equality

There are four main Properties of Equality that we use when solving linear equations.

Properties of Equality
Addition Property of Equality	If a=b, then a+c=b+c.
Subtraction Property of Equality	If a=b, then a-c=b-c.
Multiplication Property of Equality	If a=b, then ac=bc.
Division Property of Equality	If a=b and c is not 0, then ac= bc.