Answer:
Range = [- 2.5, 0.5] = [ - 5/2, 1/2]
Explanation:
Smallest value of cos α = - 1,
largest value of cos α = 1.
When cos 4x = - 1, y=3/2cos4x-1 = 3/2*(-1) - 1 = - 5/2 = - 2 1/2 = - 2.5
When cos 4x = 1, y=3/2cos4x-1 = 3/2*1 - 1 = 1/2 = 0.5
Range = [- 2.5, 0.5] = [ - 5/2, 1/2]