F flakine Junior Member Joined Aug 24, 2005 Messages 78 Mar 6, 2006 #1 If y=x^3+2x and dx/dt=5, find dy/dt when x=2. Why can't you that the deriv of y (2x^2+2) and substitute for x?
If y=x^3+2x and dx/dt=5, find dy/dt when x=2. Why can't you that the deriv of y (2x^2+2) and substitute for x?
J jacket81 Junior Member Joined Oct 12, 2005 Messages 75 Mar 6, 2006 #2 Well, wouldn't dy/dx=3x^2+2, so then dy/dt=(dy/dx)(dx/dt) = (3x^2+2)5 = 15x^2+10. So, then substitute in x=2.
Well, wouldn't dy/dx=3x^2+2, so then dy/dt=(dy/dx)(dx/dt) = (3x^2+2)5 = 15x^2+10. So, then substitute in x=2.
