For
f(x) = x2 + 8x + 9,
evaluate
f(x + 2) − f(x).
Simplify.

f(x) = x² + 8x + 9, f(x + 2) - f(x)

                     ↓

                4x + 20

explanation:

previous steps have made pa≅ pb ≅ st ≅ su. setting the compass width to ab allows you to make tu the same length. then δstu ≅ δpab by the sss congruence postulate, and ∠p ≅ ∠s by the reason cpctc.