cos^2a-sin^2a=多少?

cos^2a-sin^2a=多少? 求证1+sin a+cos a+2sin acos a/1+sin a+cos a=sin a+cos a 求证:sin 2a/1+sin a+cos a=sin a+cos a-1急 sin^4+sin^2cos^2+cos^2a= 一个简单的三角函数题(sin a + cos a)/(sin a - cos a) 则 sin a *cos a=(sin a + cos a)/(sin a - cos a) = 2 则 sin a *cos a= 证明Cos^A-Sin^A=1-2Sin^A=2Cos^A-1=cos^a-sin^a cos^2a+sin^2a=? sin^2A/cos^2A=? 求证 1+sin a+cos a+2sin a*cos a/1 +sin a +cos a = sin a+ cos a 有什么思路! 如果2sin a=cos a,那么cos^2等于多少? tan a=2,(3sin a-cos a)/(2sin a+cos a)= 已知tan a=2,求sin a+cos a /cos a -sin a 的值 已知tan(a)=3,求sin^2(a)+2sin(a)cos(a)+3cos^2(a)/sin(a)cos(a)+cos^2(a)的值 cos A/2等于多少还有sin A/2等于 cos A/2等于多少还有sin A/2等于 sin 2a+2sin方a/ 1+tan a =2sin a cos a sin^4a-cos^4a=sin^2a-cos^2a 证明sin^4a-cos^4a=sin^2a-cos^2a