化简sina^8-cosa^8-sin^6a+cos^6a+sin^4a

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化简sina^8-cosa^8-sin^6a+cos^6a+sin^4a
化简sina^8-cosa^8-sin^6a+cos^6a+sin^4a

化简sina^8-cosa^8-sin^6a+cos^6a+sin^4a
令 x=(sin a)^2,
则 (cos a)^2 =1-x.
所以原式 =x^4 -(1-x)^4 -x^3 +(1-x)^3 +x^2
=[ x^2 +(1-x)^2 ] [ x^2 -(1-x)^2 ] -x^3 +(1 -3x +3x^2 -x^3) +x^2
=(2x^2 -2x +1) (2x -1) -2x^3 +4x^2 -3x +1
=2x^3 -2x^2 +x
=2 (sin a)^6 -2 (sin a)^4 +(sin a)^2
= = = = = = = = =
换元法,注意次数.
可惜最后更麻烦,再检查一下题目.

化简sina^8-cosa^8-sin^6a+cos^6a+sin^4a 化简cosA+sinA-1,只含sin 化简(1-sina-cosa)(1-sina+cosa)/sin²a-sina sina(cosa)^3=1/4sin 2a+1/8sin 4a证明过程化简cosA+sinA/cosA-sinA sina+sina^2=1,化简cosa^2+cos^6+cosa^8 已知sina cosa=1/8,则cosa-sina=? 若sin(cosa)cos(sina) 比较大小:cosa,cos(sina),sin(cosa) 为什么4cosa+3sina-8=5sin(a+b)-8 化简sin(a-b)*cosa - cos(a-b)*sina Sin^4a+Sina*Cosa+Cos^2a化简化简[sin(60+a)+cos120*sina]/cosa=? 化简:（sina+cosa)2一2sin a cos a 已知sin a*cos a=1/8,且a为锐角,则sina+cosa=? 三角恒等式的问题若 sinA:sin(A/2)=8:5则cosA=? 若sina:cos(a/2)=8:5,则cosa=有助于回答者给出准确的答案若sina:sin(a/2)=8:5,则cosa= 已知a为第三象限角,且sina-cosa=根号3/3（1）求sina+cosa?（2）5sin^2a/2+8sina/2cosa/2+11cos^2a/2-8的值.