Find dy/dt?

Question

 

Find dy/dt, given that y=x^2+4x and x=cos(3t).

Answer 1

dy/dt

=(dy/dx)(dx/dt)

= (2x+4)(-sin(3t))(3)

= -6(cos(3t)+2)(sin(3t))

 

or

y = cos^2(3t)+4cos(3t)

dy/dt

= 2cos(3t)(-sin(3t)(3) - 12sin(3t)

= -6(cos(3t)+2)(sin(3t))