\[ 19. f(x) = 5x^{2}\] \[ \frac {d}{dx}(5x^{2})\]
\[ = 5 \frac {d}{dx}(x^{2})\]
\[ = 5 * 2x^{2-1} = 10x \]
\[ 20. f(x) = (x-2)^{3}\]
\[ f = u^{3}, u = (x-2)\]
\[ \frac {d}{du}(u^{3}) \frac {d}{dx}(x-2)\]
\[ 3u^{2} * 1 = 3(x-2)^{2} \]