已知sin(π/4--x)=5/13,0
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![已知sin(π/4--x)=5/13,0](/uploads/image/z/657632-56-2.jpg?t=%E5%B7%B2%E7%9F%A5sin%28%CF%80%2F4--x%29%3D5%2F13%2C0)
已知sin(π/4--x)=5/13,0
已知sin(π/4--x)=5/13,0
已知sin(π/4--x)=5/13,0
sin(π/4-x)=5/13
0<x<π/4
0<π/4-x
cos(π/4-x)=12/13
sin(π/4-x)
=sinπ/4cosx-cosπ/4sinx
=√2/2cosx-√2/2sinx
=√2/2(cosx-sinx)=5/13
两边平方
1/2(cosx-sinx)^2=25/169
1-2sinxcosx=50/169
sin2x=119/169
sin2x/cos(π/4-x)
=(119/169)/(12/13)
=119/156