已知sin(x-π/4)=3/5,∈(π/4,π/2),求cos2x的值?如题.是x∈(π/4,π/2)
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已知sin(x-π/4)=3/5,∈(π/4,π/2),求cos2x的值?如题.是x∈(π/4,π/2)
已知sin(x-π/4)=3/5,∈(π/4,π/2),求cos2x的值?
如题.
是x∈(π/4,π/2)
已知sin(x-π/4)=3/5,∈(π/4,π/2),求cos2x的值?如题.是x∈(π/4,π/2)
sin(π/6)=3/5,所以有x=π/6+π/4=5π/12
2x=5π/6
cos(2x)=cos(5π/6)=-cos(π-5π/6)=-cos(π/6)=-4/5
打字不易,
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