sin^2 (a) + cos^2 (a) 如何等于 10sin^2的sin^2 (a) + cos^2 (a) = 10sin^2 (a)= 1上面的10sin^2 (a)是怎么得来的.若已知cot a = -3,求sin tan a和cos a的值因为cot a = -3，所以tan a = 1/ cos a = 1/3因为tan a = -1/3 < 所以角a是

sin/cos^2a+cos/sin^2a最小值 求证1+sin a+cos a+2sin acos a/1+sin a+cos a=sin a+cos a 化简(sin a^2/cos a +cos a)*cot 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= sin^2(a+pai)-cos(pai+a)*cos(-a)+1 证明Cos^A-Sin^A=1-2Sin^A=2Cos^A-1=cos^a-sin^a 化简:sin(-a)cos(2π+a)sin(-a-π) 化简Sin A + Sin 2A / 1+cos A + 化简sin^2a-cos^2a cos^2a+sin^2a=? sin^2A/cos^2A=? 化简sin(a/2)cos(a/2) 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! 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 化简cos(a+b)cos(a-b)+sin^2b