-π/2

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-π/2
-π/2

-π/2
sina+cosa=-1/5
（sina+cosa）^2=(-1/5)^2
sina^2+cosa^2+2sinacosa=1/25
1+2sinacosa=1/25
2sinacosa=-24/25
(sina-cosa)^2=sina^2+cosa^2-2sinacosa=1+24/25=49/25
丨sina-cosa丨=7/5
∵ -π/2

2kπ+π π/2 π/2 -π/2 π/2 -π/2 -π/2 π/2 π/2 π/2 π/2 2/π π/2 kπ-2π/3 已知π+2Kπ Sin(π+π/6)Sin(2π+π/6)Sin(3π+π/6).Sin(2008π+π/6)求值设2kπ+π/2 为什么=2Kπ+π/2