Question

If y=(x^3)+5x and dx/dt=7. Find dy/dt when x=3

Answer 1

By the chain rule
\[ \frac{dy}{dt} = \frac{dy}{dx}\frac{dx}{dt} \] See what to do now?

Answer 2

What am I supposed to plug in?

Answer 3

Well, you are given dx/dt, so that's one piece.

And you can calculate for yourself dy/dx, no?

Answer 4

y= x^3+5x

Can you find dy/dx ? (use the power rule)

Once you have dy/dx, evaluate it at x=3
now put all the pieces together
(see JamesJ above)