已知sin(π/4-a）=5/13 a∈（0,π/4）求cos2a/cos(π/4+a)

已知sin(π/4-a）=5/13 a∈（0,π/4）求cos2a/cos(π/4+a)
已知sin(π/4-a）=5/13 a∈（0,π/4）求cos2a/cos(π/4+a)

已知sin(π/4-a）=5/13 a∈（0,π/4）求cos2a/cos(π/4+a)
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