Question

A ship is 400 miles directly north of the tahiti and is sailing south at 20mi/hr. another ship is 300 miles east of tahiti and is sailing west at 15mi/hr. at what rate is the distance between the ships changing?

Answer 1

this teacher likes negative derivatives
h^2 = x^2 + y^2
2 h dh/dt = 2 x dx/dt + 2 y dy/dt
dx/dt = -15
dy/dt = -20

h at t = 0 is 500

2 (500)dh/dt = 2 (300)(-15) + 2(400)(-20)

enough