### Home > APCALC > Chapter 12 > Lesson 12.1.2 > Problem12-27

12-27.

Multiple Choice: Which of the following equations can be used to determine where $r(θ) = 5 - 4\cos(θ)$ has a horizontal tangent?

1. $\sin(θ) = 0$

1. $5\sin(θ) = 4\sin(2θ)$

1. $5\sin(θ) = 2\sin(2θ)$

1. $5\cos(θ) = 2\cos(2θ)$

1. $5\cos(θ) = 4\cos(2θ)$

This is when $dy/dθ = 0$.

$y = r\sin(\theta)=(5-4\cos(\theta))\sin(\theta)$

You will need to use a double angle identity to rewrite your $y =$ equation or your final answer.