Question

differentiate y=3x^4cosxsinx

Answer 1

Use product rule. First term times derivative of second term + second term times derivative of first term.
$y=(3x^4)(cosxsinx)$
$y'=3x^4(cosx*cosx+sinx*-sinx)+(cosxsinx)(12x^3) \\ y'=3x^4cos^2x-3x^4sin^2x+12x^3cosxsinx$