Свойства производной:
1) y' = (ab)' = b*a' + a*b'
2) (y(f(x)))' = y'(f(x)) * f '(x)
a = e^(3x+1)
b = cos^2(5x)
y' = 3e^(3x+1)*cos^2(5x) + 2cos(5x)*(-sin(5x))*5*e^(3x+1) = 3e^(3x+1)*cos^2(5x) - 10cos(5x)*sin(5x)*e^(3x+1) = e^(3x+1)*cos^2( 5x)*(3 - 10sin(5x))