题目
已知函数. (Ⅰ)求f(x)的最大值及最小正周期; (Ⅱ)求使f(x)≥2的x的取值范围 答案:解:(Ⅰ)∵f(x)=sin(2x+)+sin(2x-)+2cos2x =sin2xcos+cos2xsin+sin2xcos-cos2xsin+cos2x+1 =sin2x+cos2x+1 = 2sin(2x+)+1 ∴f(x)max=2+1=3 (Ⅱ)∵f(x)≥2 ∴ 2sin(2x+)+1≥2 ∴sin(2x+)≥ ∴ 2kx+≤2x+≤2k+ k≤在Rt△ABC中,∠C=90°,AB=13,AC=12,则cosB= ,tanB= .