sin(45+a)cos(45+a)怎么得=1/2sin(90+2a)?

证明Cos^A-Sin^A=1-2Sin^A=2Cos^A-1=cos^a-sin^a 化简Sin A + Sin 2A / 1+cos A + tan a/2=sin/1+cos a=1-cos a/sin a 求证：tan a/2＝(1-cos)/sin a=sin a/(cos a+1) 已知 sin a-cos a=1/2,则 sin^3 a-cos^3 a 若sin^4a/sin^2b+cos^4a/cos^2b=1,证明sin^4b/sin^2a+cos^4b/cos^2a 证明tan a/2=sin a/(1+cos a) 已知2cos∧2 a+3cos a sin a-3sin∧2 a=1,求:tan a,(2sin a-3cos a)\( (cos a)^4+(sin a)^2*(sin a)^2+(sin a)^2=? (1-sin^6a-cos^6a)/(sin^2a-sin^4a) 已知tan a=2,求sin a+cos a /cos a -sin a 的值 sin(45度+a)=1/3则cos(90度—2a)=