Exponential and trigonometric functions practice question 11

$f$ is a quotient whose bottom contains $\cos x$. What is the derivative of that bottom, sign included, and where does it enter the rule?

Quotient rule. The derivative of the denominator is $-\sin x$, so watch the double negative.

At $x = \dfrac{\pi}{2}$: $\cos\dfrac{\pi}{2} = 0$ and $\sin\dfrac{\pi}{2} = 1$. Remember to square the denominator.