0<a<派/4,sin(派/4-a)=5/13,求cos2a/cos(派/4+a)的值.
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0<a<派/4,sin(派/4-a)=5/13,求cos2a/cos(派/4+a)的值.
0<a<派/4,sin(派/4-a)=5/13,求cos2a/cos(派/4+a)的值.
0<a<派/4,sin(派/4-a)=5/13,求cos2a/cos(派/4+a)的值.
sin(派/4-a)=5/13
cos(派/4-a)=12/13
sin(派/2-2a)=2*5/13*12/13=120/169=cos2a
cos(派/4+a)=sin(派/2-派/4-a)=sin(派/4-a)=5/13
cos2a/[cos(派/4+a)]
=120/169÷5/13
=24/13