Page 120 - Algebra 1

Solving Equations by Adding
Solve. Then check the solution.
Example
2
a. x-3=12 SOLUTION
x - 3 = 12
+3 = +3 __ __
Add 3 to both sides to undo the subtraction.
x = 15
Check Substitute15forx.
x - 3 12 (15) - 3 12
12=12 ✓
Caution
Sometimes the variable is on the right side of the equal sign. Use inverse operations to isolate the variable.
b. -15=n-8 SOLUTION
-15 = n - 8
+8 = +8 __ __
Add 8 to both sides.
-7 = n
Check Substitute-7forn.
-15 (-7) - 8 -15 = -15 ✓
Math Reasoning
Justify Does it matter if you add (–7) to each side or subtract 7 from each side? Explain.
Example
3
Solve.
a. k+7=13 SOLUTION
k + 7 = 13
-7 = -7 __ __
k=6
b. -21=p+9 SOLUTION
-21 = p + 9
-9 = -9 __ __
-30 = p
Solve Equations by Subtracting
Subtract 7 from both sides.
Subtract 9 from both sides.
Lesson 19 105