若0

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若0若0若0∵1=sin²x+cos²x≥2sinxcosx∴sinxcosx≤1/2∴1/(sinxcosx)≥2f(x)=1+1/sinx+1/cosx+1/(sinxcosx

若0
若0

若0
∵1=sin²x+cos²x≥2sinxcosx
∴sinxcosx≤1/2
∴1/(sinxcosx)≥2
f(x)=1+1/sinx+1/cosx+1/(sinxcosx)≥1+2√[1/(sinxcosx]+1/(sinxcox)≥1+2√2+2=3+2√2