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函数y=(sin^2+1)(cos^2+3)

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函数y=(sin^2+1)(cos^2+3)
函数y=(sin^2+1)(cos^2+3)
的最大值是?
函数y=(sin^2+1)(cos^2+3)
y=(sin^2+1)(cos^2+3)
=sin^2·cos^2+3sin^2+cos^2+3
=sin^2·cos^2+2sin^2+(sin^2+cos^2)+3
=sin^2·cos^2+2sin^2+4, 因为sin^2+cos^2=1,移项,cos^2=1-sin^2
=sin^2(1-sin^2)+2sin^2+4
= -(sin^2)^2+3sin^2+4
即求F(x)=-x^2+3x+4 ,(0≤x≤1,因为0≤sin^2≤1)的最大值
二次函数因该会吧?F(x)最大=F(1)=6,
即y=(sin^2+1)(cos^2+3)最大值是6,当sin^2=1,cos^2=0时取得