Addition and subtraction of powers follow the same rules as algebraic expressions, ${a}^{b}+{a}^{b}=2{a}^{b}$. You do the same if the power consists of numbers instead of a symbols.

Example 1

Calculate ${3}^{2}+{3}^{2}$

You use what you have learned in algebra and get

 ${3}^{2}+{3}^{2}=2×{3}^{2},$

which is not the same as ${6}^{2}=6×6=36$, but

 $2×\underset{3×3}{\underbrace{{3}^{2}}}=2×9=18.$

Subtraction is the same: $\begin{array}{llll}\hfill {b}^{2}-{b}^{2}& =0,\phantom{\rule{2em}{0ex}}& \hfill & \phantom{\rule{2em}{0ex}}\\ \hfill -{b}^{2}-{b}^{2}& =-2{b}^{2}.\phantom{\rule{2em}{0ex}}& \hfill & \phantom{\rule{2em}{0ex}}\end{array}$