已知sin(π/4-a)=5/13,a∈(0,π/4),求cos2a/cos(π/4+a)的值
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![已知sin(π/4-a)=5/13,a∈(0,π/4),求cos2a/cos(π/4+a)的值](/uploads/image/z/1241510-14-0.jpg?t=%E5%B7%B2%E7%9F%A5sin%28%CF%80%2F4-a%29%3D5%2F13%2Ca%E2%88%88%EF%BC%880%2C%CF%80%2F4%EF%BC%89%2C%E6%B1%82cos2a%2Fcos%28%CF%80%2F4%2Ba%29%E7%9A%84%E5%80%BC)
已知sin(π/4-a)=5/13,a∈(0,π/4),求cos2a/cos(π/4+a)的值
已知sin(π/4-a)=5/13,a∈(0,π/4),求cos2a/cos(π/4+a)的值
已知sin(π/4-a)=5/13,a∈(0,π/4),求cos2a/cos(π/4+a)的值
cos(π/4+a)=cos(π/2-(π/4-a))=sin(π/4-a)=5/13
已知展开化简
cosa-sina=5√2/13两侧平方化简
sin2a=119/169
可得
cos2a=120/169
原式=24/13