Consider the function, y=2*root2+4cos(2x-pi/2)?

0 ≦ x < π
0 ≦ 2x < 2π
- π/2 ≦ 2x - π/2 < (3/2)π

y = 2√2 + 4*cos ( 2x - π/2 ) = 0
cos ( 2x - π/2 ) = - 2√2 / 4 = - 1/√2
2x - π/2 = (3/4)π , (5/4)π
2x = (5/4)π , (7/4)π
x = (5/8)π , (7/8)π ..... Ans