Question

In the following exercises, add or subtract the monomials.

$\begin{array}{l}\left(a\right)7x^2+5x^2\\ \left(b\right)4a-9a\end{array}$

Short answer

The result of solving is

$\begin{array}{l}a)12x^2\\ b)-5a\end{array}$

Step-by-step solution

Step 1. Given information 

$\begin{array}{l}\text{Thegivenexpressionsare}\\ \left(a\right)7x^2+5x^2\\ \left(b\right)4a-9a\\ \text{Wehavetoaddorsubtractthegivenexpressionsasapplicable.}\end{array}$

Step 2. Solve for part (a)

$\begin{array}{l}\text{Considerthegivenexpression}\\ \Rightarrow 7x^2+5x^2=\left(7+5\right)x^2\\ =12x^2\end{array}$

Step 3. Solve for part (b)

$\begin{array}{l}\text{Considerthegivenexpression}\\ \Rightarrow 4a-9a=\left(4-9\right)a\\ =-5a\end{array}$