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Questions  

If ϕ(x) is a polynomial function and ϕ(x)>ϕ(x)  x1 and ϕ(1)=0,then 

a
ϕ(x)≥0   ∀x≥1
b
ϕ(x)<0   ∀x≥1
c
ϕ(x)=0  ∀x≥1
d
none of these

detailed solution

Correct option is A

Given ϕ′(x)−ϕ(x)>0 ∀x≥1or      e−xϕ′(x)−ϕ(x)>0 ∀x≥1or     ddxe−xϕ(x)>0 ∀x≥1Therefore,  e−xϕ(x)) is an increasing function ∀x≥1.Since ϕ(x) is a polynomial,       e−xϕ(x)>e−1ϕ(1) or e−xϕ(x)>0 [∵ϕ(1)=0]or    ϕ(x)>0

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