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Questions  

If f:RR is defined by f(x)=x2+1 then value of f1(17) and f1(3) are, respectively.

a
ϕ,{4,−4}
b
ϕ, {3,−3}
c
{{3,−3}, ϕ
d
{4,−4}, ϕ

detailed solution

Correct option is D

For any A⊆R, we have f−1(A)={x∈R:f(x)∈A}. Thus, f−1(17)={x:f(x)∈{17}}={x:f(x)=17}=x:x2+1=17={4,−4}.and similarly, ∣f−1(−3)=x∈R:x2+1=−3=ϕ

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