sin(a+105)cos(a-15)-cos(a+105)sin(a-15)

sin(a+105度)cos(a-15度)-cos(a+105度)sin(a-15度) 化简cos^2(a+15)+sin^2(a-15))+sin(a+180)cos(a-180) 化简~cos^2(a+15)+sin^2(a-15)+sin(a+180)cos(a-180) 化简sin a+cos a 化简sin(a-15度)cos（a+15度）+cos（a-15度)sin(a+15度) 化简：[cos(a+15度)]^2+[sin(a-15度)]^2+[sin(a+180度)]*[cos(a-180度)] 4.9-1/化简：[cos(a+15度)]^2+[sin(a-15度)]^2+[sin(a+180度)]*[cos(a- 化简cos(15°+a)sin(45°+a)-cos(75°-a)sin(45°-a) 已知 sin a,sin 2x ,cos a 成等差数列,sin a ,sin x ,cos a 成等比数列,求cos 利用三角函数定义证明cos a-sin a+1/(cos a+sin a+1)=1-sin a/cos a 证明Cos^A-Sin^A=1-2Sin^A=2Cos^A-1=cos^a-sin^a cos平方a-sin平方a为什么等于cos平方a-sin平方a/cos平方a+sin平方a