所以c=2b-a=b+(b-a)<b<a
所以a最大
则A=120
b=a-4
c=2b-a=a-8
cosA=-1/2=(b2+c2-a2)/2bc
b2+c2-a2=-bc
则a2-16a+64+a2-8a+16-a2=-a2+12a-32
a2-18a+56=0
a=4,a=14
c=a-8>0
所以a=14
b=a-4=10
c=a-8=6
导函数为：y‘=4[sin(x/4)]^3*cos(x/4)*1/4+4[cos(x/4)]^3*[-sin(x/4)]*1/4
=sin(x/4)cos(x/4)*[sin(x/4)^2-cos(x/4)^2]
=1/2*sin(x/2)*[-cos(x/2)]
=-1/4*sinx
=4sin^3 xcosx-4cos^3 xsinx本回答被网友采纳
求解(y=sin^4(X\/4)+cos^4(X\/4)的导数)
a2-18a+56=0 a=4,a=14 c=a-8>0 所以a=14 b=a-4=10 c=a-8=6
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