sin a/2—cos a/2=1/5 求sin a

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 已知sin a+cos a= -1/5 求1）sin acos a 2）sin a-cos a sin a/2—cos a/2=1/5 求sin a 证明Cos^A-Sin^A=1-2Sin^A=2Cos^A-1=cos^a-sin^a sin(a-b)*cos a-cos(a-b)*sin a=1/5,则cos 2b的值是 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! Cos(a+b)*cos(a-b)=1/5 求cos ^2-sin^2 已知tan a=-1/3,求4sin a-2cos a/5cos a+3sin a= sin 2a+2sin方a/ 1+tan a =2sin a cos a tan a/2=sin/1+cos a=1-cos a/sin a tan a =3求4sin a-2cos a/5cos+3sin a 求证：tan a/2＝(1-cos)/sin a=sin a/(cos a+1) sin a/(1+cos a)=1/2,求sin a+cos a 已知 sin a-cos a=1/2,则 sin^3 a-cos^3 a sin a-cos a=1/5 sin^2 a+cos^2 a=1 可以的话给先过程 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(1-sin^6 a-cos^6 a)/(cos^2 a-cos^4 a)==