三角恒等变换习题cos(x-y)=√5/5 ,cos2x=√10/10 ,并且x,y均为锐角,且x

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三角恒等变换习题cos(x-y)=√5/5,cos2x=√10/10,并且x,y均为锐角,且x三角恒等变换习题cos(x-y)=√5/5,cos2x=√10/10,并且x,y均为锐角,且x三角恒等变换

三角恒等变换习题cos(x-y)=√5/5 ,cos2x=√10/10 ,并且x,y均为锐角,且x
三角恒等变换习题
cos(x-y)=√5/5 ,cos2x=√10/10 ,并且x,y均为锐角,且x

三角恒等变换习题cos(x-y)=√5/5 ,cos2x=√10/10 ,并且x,y均为锐角,且x
【解】C
cos(x-y)=√5/5且x sin(x-y)=-2√5/5
cos2x=√10/10 ==> sin2x=3√10/10
∵x+y=2x-(x-y)
∴cos(x+y)=cos[2x-(x-y)]
=cos2xcos(x-y)+sin2xsin(x-y)
=√10/10×√5/5+3√10/10×(-2√5/5)
=-√2/2
∵x,y都是锐角
∴(x+y)=3π/4