已知sin(a+135°)=5/13,cos(45°-β ),且-45°cos(45°-β )=3/5

问题描述:

已知sin(a+135°)=5/13,cos(45°-β ),且-45°
cos(45°-β )=3/5

cos2(a-β)=2cos^2(a-β)-1
-45°