已知f(x)=cosx+sin^2x,求f(派\6)求最大值最小值
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人气:228 ℃ 时间:2019-11-19 04:51:31
解答
f(x)=cosx+sin^2x
=cosx+1-cos^2x
=-cos^2x+cosx+1
f(π/6) =-cos^2(π/6)+cos(π/6)+1=-3/4+根号3/2+1=根号3/2+1/4
设t=cosx ,t∈[-1,1]
g(t)=-t^2+t+1
=-(t-1/2)^2+1/4+1
=-(t-1/2)^2+5/4
t=1/2时,取得最大值5/4
t=-1时,取得最小值-1
所以f(x)最大值5/4;最小值-1
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