求下面三角函数的单调区间函数y=sin(-2x)的单调增区间是函数y=log0.5 (sin(2x+四分之π))的单调减

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  • 函数y=sin(-2x)的单调增区间是y=sin(-2x)=-sin2x;由2kπ+π/2≦2x≦2kπ+3π/2,得单调增区间为:kπ+π/4≦x≦kπ+3π/4,k∊z.函数y=log₁/₂ [sin(2x+π/4)]的单调减区间设y=log₁/₂u,u=sin(2x+π/4);y是u的减函数,u是x的正弦函数;要使y=f(x)单调减,必需选择u关于x单调增的区间(同增异减):故由2kπ-π/2≦2x+π/4≦2kπ+π/2,得2kπ-3π/4≦2x≦2kπ+3π/4,得单调增区间为:kπ-3π/8≦x≦kπ+3π/8,k∊z..