已知cos(x-π/4)=根号2/10,x属于(π/2,3π/4) 求.sin(2x+π/3)的值.

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已知cos(x-π/4)=根号2/10,x属于(π/2,3π/4)求.sin(2x+π/3)的值.已知cos(x-π/4)=根号2/10,x属于(π/2,3π/4)求.sin(2x+π/3)的值.已知

已知cos(x-π/4)=根号2/10,x属于(π/2,3π/4) 求.sin(2x+π/3)的值.
已知cos(x-π/4)=根号2/10,x属于(π/2,3π/4) 求.sin(2x+π/3)的值.

已知cos(x-π/4)=根号2/10,x属于(π/2,3π/4) 求.sin(2x+π/3)的值.
π/2π/4因为cos(x-π/4)=√2/10
所以sin(x-π/4)=√98/10
那么tan(x-π/4)=√(98/2)=7
(tanx-1)/(1+tanx)=7
解得
tanx=-4/3
sin2x=2tanx/(1+tan²x)=-24/25
cos2x=(1-tan²x)/(1+tan²x)=-7/25
sin(2x+π/3)=sin2xcosπ/3+cos2xsinπ/3=(-24/25)×(1/2)+(-7/25)×(√3/2)
=-(24+7√3)/50

arccos(√2/10)=81.87度
81.87+排/4>排
所以这个题目有问题