求证sin^4a+cos^4a=1-2sin²acos²a对于这类题目不是很会 求方法

求证3-sin^4a-cos^4a/2cos^a=1+tan^a+sin^a 速答 谢谢 求证2cos^2a+sin^4a=cos^4a+1 求证sin^4a+cos^4a=1-2sin^2acos^2a 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 求证sin^4a+cos^4a=1 求证1/sin^2a+3/cos^2a>=4+2根号下31/sin²a +3/cos²a=(sin²a+cos²a)/sin²a +3(sin²a+cos²a)/cos²a=1+cos²a/sin²a+3+3sin²a/cos²a=4+cos²a/sin²a+3sin²a/cos²a≥4+2√[(cos 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! sin∨4a-cos∨4a=sin²a-cos²a 求证 求证：tan a/2＝(1-cos)/sin a=sin a/(cos a+1) cos^4a/(cos^2b)+sin^4a/(sin^2a)=1 求证cos^4b/(cos^2a)+sin^4a/(sin^2b)=1 求证sin^4a-cos^4a=-cos2a如题 求证 sin^4(a)-cos^4(a)=-cos(2a) 已知sin^4a/cos^2b+cos^4a/sin^2b=1,求证:sin^4 b/cos^2 a+cos^4b/sin^2a=1 已知(cos^4a)/cos^2b+(sin^4a)/sin^2b=1求证(cos^4b)/cos^2a+(sin^4b)/sin^2a=1 三角函数 求证:cos^2(a)-cos(2a)*cos(4a)=sin^2(3a)求证:cos^2(a)-cos(2a)*cos(4a)=sin^2(3a) 求证:sin a (1+cos2a)=sin a cos a 求证 sin~4a-cos~4a=sin~2a-cos~2a tan~2asin~2a=tan~2a-sin~2a 求证2(1+cosa)-sin∧2a=4cos∧4a/2