Question

If x^2 + xy = 20 and dx/dt = -4 when x = -5 and y = 1, what is dy/dt

Answer 1

3.2

Explanation:

x² + xy = 20

Take the derivative with respect to time:

2x dx/dt + x dy/dt + y dx/dt = 20

(2x + y) dx/dt + x dy/dt = 20

Given x = -5, y = 1, and dx/dt = -4:

(2(-5) + 1) (-4) + (-5) dy/dt = 20

(-10 + 1) (-4) − 5 dy/dt = 20

36 − 5 dy/dt = 20

5 dy/dt = 16

dy/dt = 3.2