## Calculus (3rd Edition)

$(fg)'(4)=-20$ $(f/g)'(4)=0$
Using the product rule, we have $(fg)'(4)=g(4)\cdot f'(4)+f(4)\cdot g'(4)=(5\times-2)+(10\times-1)=-20$ Using the quotient rule, we obtain $(\frac{f}{g})'(4)=\frac{g(4)\cdot f'(4)-f(4)g'(4)}{(g(4))^{2}}=\frac{(5\times-2)-(10\times-1)}{5^{2}}=0$