因为sin^2a+cos^2a+2sinacosa=4/9所以1+sin2a=4/92sinacosa为什么等于sin2a

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 求证:sin 2a/1+sin a+cos a=sin a+cos a-1急 sin^4+sin^2cos^2+cos^2a= 化简:sin(-a)cos(2π+a)sin(-a-π) 化简Sin A + Sin 2A / 1+cos A + 三角形ABC中,A,B为锐角,sin(A+B)=sinA^2+sinB^2,判断三角形ABC的形状因为 (sin A)^2 +(sin B)^2 =sin (A+B)=sin A cos B +sin B cos A,所以 sin A (sin A -cos B) +sin B (sin B -cos A) =0.(*)又因为 A,B 为锐角,所以 sin A>0,sin B>0.(1) 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 化简sin^2a-cos^2a cos^2a+sin^2a=? sin^2A/cos^2A=? 化简sin(a/2)cos(a/2) sin 2a+2sin方a/ 1+tan a =2sin a cos a 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! 证明 sin^2A+sin^2B-sin^2A*sin^2B+cos^2A*cos^2证明 sin^2A+sin^2B-sin^2A*sin^2B+cos^2A*cos^2B=1 化简(sin a^2/cos a +cos a)*cot a 化简sin^2a+sin^2b-sin^2a*sin^2b+cos^2a*cos^2b