证明sin^4a-cos^4a=sin^2a-cos^2a

证明sin(4A)sin(2A)(1-cos(2A)) cos(4A)cos(2A)(1 cos(2A))=cos(2A 若sin^4a/sin^2b+cos^4a/cos^2b=1,证明sin^4b/sin^2a+cos^4b/cos^2a 证明Cos^A-Sin^A=1-2Sin^A=2Cos^A-1=cos^a-sin^a 证明tan a/2=sin a/(1+cos a) 化简(1-sin^6 a-cos^6 a)/(cos^2 a-cos^4 a)== (cos a)^4+(sin a)^2*(sin a)^2+(sin a)^2=? 证明:cos^4 a-sin^4 a=cos^2 a(1-tan a)(1+ tan a) 证明： sin^2a+cos^2a=1 已知(4sin a－2cos a)／(5cos a +3sin a)=6/11,求cos＾4 a－sin＾4 a 已知sin a-2cos a=0 求4sin^2 a-3sin a x cos a-5cos^2 a的值 tan a/2=(1-cos a)/sin a=sin a/(1+cos a)如何证明? 已知a(-0,兀且2SIN A-SIN ACOS A-3COS A=0求SIN(+兀/4)/SIN 2A+COS 2A+