已知pi/4<a<b<pi/2,且sin(a+b)=4/5,cos(a-b)=12/13,求sina2a的值.
我想知道a-b定号怎么定,
人气:386 ℃ 时间:2020-06-18 21:12:24
解答
已知pi/4<a<b<pi/2,且sin(a+b)=4/5,cos(a-b)=12/13,则
cos(a+b)=-3/5,sin(a-b)=-5/13
sina2a=sin(a+b)cos(a-b)+cos(a+b)sin(a-b)=63/65
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