### Learning Outcomes

• Subtract polynomials

In a previous lesson, you learned how to simplify expressions by combining like terms. Adding and subtracting monomials is the same as combining like terms. Like terms must have the same variable with the same exponent. Recall that when combining like terms only the coefficients are combined, never the exponents.

### example

Add: $17{x}^{2}+6{x}^{2}$

Solution

 $17{x}^{2}+6{x}^{2}$ Combine like terms. $23{x}^{2}$

### example

Subtract: $11n-\left(-8n\right)$

### example

Simplify: ${a}^{2}+4{b}^{2}-7{a}^{2}$

### try it

Watch the following video for more examples of how to multiply polynomials.

Adding and subtracting polynomials can be thought of as just adding and subtracting like terms. Look for like terms—those with the same variables with the same exponent. The Commutative Property allows us to rearrange the terms to put like terms together. It may also be helpful to underline, circle, or box like terms.

### Example

Find the sum: $\left(4{x}^{2}-5x+1\right)+\left(3{x}^{2}-8x - 9\right)$.

### try it

Parentheses are grouping symbols. When we add polynomials as we did in the last example, we can rewrite the expression without parentheses and then combine like terms. But when we subtract polynomials, we must be very careful with the signs.

### example

Find the difference: $\left(7{u}^{2}-5u+3\right)-\left(4{u}^{2}-2\right)$.

### Exercises

Subtract $\left({m}^{2}-3m+8\right)$ from $\left(9{m}^{2}-7m+4\right)$.