197. Find the derivative of the function $y=9 x^{5}$.
Solution. Using rule V and the formula $\left(x^{n}\right)^{\prime}=n x^{n-1}$, we get

$$
y^{\prime}=\left(9 x^{5}\right)^{\prime}=9 \cdot 5 x^{4}=45 x^{4}
$$

When skilled, intermediate steps can be skipped:

$$
\left(9 x^{5}\right)^{\prime}=45 x^{4}
$$