To add or subtract like terms, add or subtract the numerical coefficients and
use the same variables.
EXAMPLE
Add 7yþ3y.
SOLUTION
7yþ3y¼ð 7 þ 3 Þy
¼10y
EXAMPLE
Subtract 8x5x.
SOLUTION
8x5x¼ð 8 5 Þx
¼3x
Adding or subtracting like terms is often called ‘‘combining like terms.’’
EXAMPLE
Combine like terms: 9xþ7x3x2x.
SOLUTION
9xþ7x3x2x¼ð 9 þ 7 3 2 Þx:
¼11x
Unlike terms cannot be added or subtracted. When an expression has both
like and unlike terms, it can be simplified by combining all like terms.
EXAMPLE
Combine like terms: 6x8xþ2y3yþ5x4y.
SOLUTION
6x8xþ2y3yþ5x4y¼6x8xþ5xþ2y3y4y
¼ð 6 8 þ 5 Þxþð 2 3 4 Þy
¼3xþð 5 Þy
¼3x5y
CHAPTER 7 Expression and Equations 131