SIN4次方—COS4次方及化简结果

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SIN4次方—COS4次方及化简结果
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SIN4次方—COS4次方及化简结果
SIN4次方—COS4次方
及化简结果

SIN4次方—COS4次方及化简结果
SIN4次方—COS4次方
=(sin²x+cos²x)(sin²x-cos²x)
=sin²x-cos²x
=1-cos²x-cos²x
=1-2cos²x
=cos2x

sin^4(a)-cos^4(a)=(sin^2(a)+cos^2(a))(sin^2(a)-cos^2(a))
=sin^2(a)-cos^2(a)=1-2cos^2(a)
=1-(1+cos(2a))
=-cos2a

(sinx)^4-(cosx)^4
=[(sinx)^2+(cosx)^2](sinx+cosx)(sinx-cosx)
=(sinx+cosx)(sinx-cosx)
=√2sin(x+π/4)*[-√2cos(x+π/4)]
=-2sin(x+π/4)*cos(x+π/4)
=-sin(2x+π/2)
=-cos2x