Did I differentiate these two functions correctly?

Question

y=2cos(2x)cos(14x)
y'=-14 sin⁡(14x)2 cos⁡(2x)-4 sin⁡(2x)cos⁡(14x)

y=2[cos 1/2(f1-f2 )x][cos 1/2(f1+f2 )x]
y^'=-[(f1+f2 )/2]sin[(f1+f2 )/2 x]2cos⁡[(f1-f2 )/2 x] - [2(f1-f2 )/2]sin[(f1-f2 )/2 x]cos ⁡[(f1+f2)/2 x]

Answer 1

they appear correct