f(x) = 5sin[2(x + 45°)]
f(x) = 5cos[90°  2(x + 45°)]
f(x) = 5cos(2x)
f(x) = 5cos(2x)

sin ( 2x + 90 )° = sin 2x cos 90° + + cos 2x sin 90 ° = cos 2x
f (x) = cos 2x°