Let a be a constant and a > 1, 0 ≤ x ≤ 2 π, then the maximum value of F (x) = cos2x + 2asinx-1 is () A. 2a+1B. 2a-1C. -2a-1D. a2

Let a be a constant and a > 1, 0 ≤ x ≤ 2 π, then the maximum value of F (x) = cos2x + 2asinx-1 is () A. 2a+1B. 2a-1C. -2a-1D. a2

F (x) = cos2x + 2asinx-1 = 1-sin2x + 2asinx-1 = - (sinx-a) 2 + A2, ∵ 0 ≤ x ≤ 2 π, ∵ - 1 ≤ SiNx ≤ 1, and ∵ a > 1, so when SiNx = 1, the maximum value is ∵ f (x) max = - (1-A) 2 + A2 = 2a-1