If x is the minimum internal angle of a triangle, then the maximum value of the function y = SiNx + cosx + sinxcosx is () A. -1B. 2C. −12+2D. 12+2
Y = SiNx + cosx + sinxcosx = SiNx (1 + cosx) + 1 + cosx-1 = (1 + SiNx) (1 + cosx) - 1 ≤ 12 [(1 + SiNx) 2 + ((1 + cosx) 2] - 1 (if and only if 1 + SiNx = 1 + cosx, then SiNx = cosx = 22), that is, y (max) = 2 + 12, so D is selected
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