y^2+xy-3x=-5

Question

dy/dt=-4
x=3
y=1
find dx/dt.
i tried doing 2y(dy/dt)+ydx/dt-3=0 but i am not getting the right answer. Please tell me where i am going wrong.

Answer 1

your derivative is wrong, the xy needs a product rule

2y dy/dt + x dy/dt + y dx/dt - 3dx/dt = 0
plugging in our stuff

2 (-4) + 3(-4) + 1(dx/dt) - 3 dx/dt = 0
-2 dx/dt = 20
dx/dt = -10

Answer 2

you need to use the product rule for xy

x dy/dt + y dx/dt

Answer 3

Thank you for the help! Completely forgot about that rule... woops