sin(45+a)cos(45+a)=1/3 怎么推出sin(90+2a)=2/3

8sin(45+a)sin(45-a)=1,sin^4a-cos^4a= 已知sin a+cos a=m求cos a-sin a(45 cos(45-a)•cos(45+a)=1/3,sin^4 a+cos^4 a=____ 求证1+sin a+cos a+2sin acos a/1+sin a+cos a=sin a+cos a sin(45+a)cos(45+a)怎么得=1/2sin(90+2a)? 求证:sin 2a/1+sin a+cos a=sin a+cos a-1急 证明Cos^A-Sin^A=1-2Sin^A=2Cos^A-1=cos^a-sin^a 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 求证:sin a (1+cos2a)=sin a cos a (sin a)/(1+cos a)=(1-cos a)/sin a怎么证sin a 1-cos a------ = -----------1+cos a sin 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! 数学三角函数计算sin(a)*cos(a)=1/8,45°＜a＜90°,求cos(a)-sin(a)的值 证明恒等式tan a*sin a/tan a-sin a=1+cos a/sin a sin(45+a)cos(45+a)=1/3 怎么推出sin(90+2a)=2/3 sin(a+45°)sin(a+15°)+cos(a+45°)cos(a+15°) tan a/2=sin/1+cos a=1-cos a/sin a sin 2a+2sin方a/ 1+tan a =2sin a cos a sin a+cos a=1/2.那么sin a*cos a=