数学化简cos15° -sin15° /cos15° +sin15°

cos15° -sin15° /cos15° +sin15°
=cos15^2-sin15^2/1+2cos15sin15
=cos30/1+sin30
=根号3/3在三角形ABC中，已知cosA=3/5,cosB=5/13求cosC麻烦给解一下这套题SINA=4/5SINB=12/13cosC=-COS(A+B)=-cosAcosB+sinAsinB=-15/65+48/65=33/65已知tan(α+β)=2/5,tan(β-180°/4)求,tan(α+180°/4)谢谢最后一题