AP Calculus BC 3.4 Differentiating Inverse Trigonometric Functions Exam Style Questions - FRQ
Question
Find the equation of the tangent line at the given point:
(a) \( y = \arctan\frac{x}{2} \) at \( \left( 2, \frac{\pi}{4} \right) \)
(b) \( y = 4x \arccos(x – 1) \) at \( (1, 2\pi) \)
(c) \( x^2 + x \arctan y = y – 1 \) at \( \left( -\frac{\pi}{4}, 1 \right) \)
▶️ Answer/Explanation
Solution
(a) \[ y’ = \frac{1/2}{1 + (x/2)^2} = \frac{2}{4 + x^2} \] At \( x = 2 \), slope \( m = \frac{1}{4} \) \[ y – \frac{\pi}{4} = \frac{1}{4}(x – 2) \]
(b) Using product rule: \[ y’ = 4\arccos(x-1) – \frac{4x}{\sqrt{2x – x^2}} \] At \( x = 1 \), slope \( m = 4\pi – 4 \) \[ y – 2\pi = (4\pi – 4)(x – 1) \]
(c) Using implicit differentiation: \[ 2x + \arctan y + \frac{x}{1 + y^2}y’ = y’ \] At \( \left( -\frac{\pi}{4}, 1 \right) \), solve for \( y’ \) to get slope \( m \)