stuck in a simple step after differentiation.

Quote:

Originally Posted by avengerevenge

pls help me with this simple step
i dont know how that last step came,

From what you have

$ y - a \sin ^3 t = - \tan t \left(x - a \cos ^3 t\right) $

$ y \cos t - a \sin^3t \cos t = - x \sin t + a \cos^3t \sin t $

$ y \cos t = - x \sin t +a \sin^3t \cos t + a \cos^3t \sin t $

$ y \cos t = - x \sin t +a \sin t \cos t\left( \underbrace{\cos^2t + \sin^2t}_{=1}\right) $

so

$ y \cos t = - x \sin t +a \sin t \cos t$ .