Question

A point is moving on y = 4 – 2x². The x-coordinate of the point is decreasing at the rate 5 unit per second then the rate at which y co-ordinate of the point is changing when the point is at (1, 2) is

• A. 5 unit/sec
• B. 15 unit/sec
• C. 10 unit/sec
• D. 20 unit/sec

Answer 1

Answer: (A)

5 unit/sec

Answer 2

y = 4– 2x²

$\frac{dy}{dt}$ = 0 – 4x $\frac{dx}{dt}$ ̃ $\frac{dy}{dt}$= – 4 × (1) × 5

̃ $\left| \frac{dy}{dt} \right|$ = 20 unit/sec