当0
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当0
当0
当0
cos2x=1-2sin^2x
2sin^2x=1-cos2x
8sin^2x=4-4cos2x
y=f(x)=(1+cos2x+8sin^2x)/sin2x
=(1+cos2x+4-4cos2x)/sin2x
=(5-3cos2x)/sin2x
=(5-3cos2x)/√[1-(cos2x)^2]
已知00
∴y>0
y*√[1-(cos2x)^2]=5-3cos2x
y^2*[1-(cos2x)^2]=(5-3cos2x)^2
(9+y^2)*(cos2x)^2-30(cos2x)+25-y^2=0
上方程未知数为(cos2x)的判别式△≥0,即
(-30)^2-4*(9+y^2)*(25-y^2)≥0
y^4-16y^2≥0
y^2*(y+4)*(y-4))≥0
y≥4(另一解y≤-4舍去)
y的最小值=4
y=4
(9+y^2)*(cos2x)^2-30(cos2x)+25-y^2=0
(5cos2x-3)^2=0
cos2x=3/5,sin2x=4/5
y=f(x)=(1+cos2x+8sin^2x)/sin2x
=(1+cos2x+4-4cos2x)/sin2x
=(5-3cos2x)/sin2x
=(5-3*3/5)/(4/5)
=4
答:当0
f(x)=(1+1-2sin^2x+8sin^2x)/2sinxcosx
=(1-3sin^2x)/sinxcosx
=(cos^2x+sin^2x-3sin^2x)/cosxsinx
=(cos^2x-2sin^2x)/cosxsinx
=cosx/sinx-2sinx/cosx
=cotx-2tanx
f(x)'=-csc^2x+sec^2x=-...
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f(x)=(1+1-2sin^2x+8sin^2x)/2sinxcosx
=(1-3sin^2x)/sinxcosx
=(cos^2x+sin^2x-3sin^2x)/cosxsinx
=(cos^2x-2sin^2x)/cosxsinx
=cosx/sinx-2sinx/cosx
=cotx-2tanx
f(x)'=-csc^2x+sec^2x=-4cot2x/sin2x
当0
(第一次打那么一堆数学符号。。。累死)
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