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若cos(派/4+x)=3/5,17派/12
人气:307 ℃ 时间:2019-12-01 13:28:52
解答
17π/12<x<7π/4,得5π/3<x+π/4<2π cos(x-π/4)=cos[(x+π/4)-π/2]=sin(x+π/4)=-√[1-cos²(x+π/4)]=-√[1-(3/5)²]=-4/5 sin(2x)=-cos(2x+π/2)=-cos[2(x+π/4)]=1-2cos²(x+π/4)=1-2•...
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