If x^2+2y=20 and dy/dt= -6 find dy/dt when x=4
looks like an oops, you have
given: dy/dt, then find dy/dt
one of them should be dx/dt
I will let you figure out which one.
x^2 + y^2 = 20
2x dx/dt + 2y dy/dt = 0
x dx/dt = -y dy/dt
when x = 4, 16+y^2 = 20
y^2 = 4
y = 2
now plug in our values into
you have 3 of the 4 values to put in
x dx/dt = -y dy/dt
solve for the missing one