WBJEE · Maths · Functions

A Mapping from IN to IN is defined as follows :
\[
\begin{aligned}
& \mathrm{f}: \mathrm{IN} \rightarrow \mathrm{IN} \\
& \mathrm{f}(\mathrm{n})=(\mathrm{n}+5)^2, \mathrm{n} \in \mathrm{IN}
\end{aligned}
\]
(IN is the set of natural numbers). Then

A \(\mathrm{f}\) is not one-to-one
B \(\mathrm{f}\) is onto
C \(\mathrm{f}\) is both one-to-one and onto
D \(\mathrm{f}\) is one-to-one but not onto

Verified Solution

Answer & Solution

Correct Answer

(D) \(\mathrm{f}\) is one-to-one but not onto

Step-by-step Solution

Detailed explanation

\begin{aligned} & \text { Hints: } \mathrm{f}: \mathrm{IN} \rightarrow \mathrm{IN} ; \mathrm{f}(\mathrm{n})=(\mathrm{n}+5)^2 \\ & \left(\mathrm{n}_1+5\right)^2=\left(\mathrm{n}_2+5\right)^2 \\ &…

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

Same subject

Explore more questions on app

From WBJEE

Explore more questions on app

A Mapping from IN to IN is defined as follows :\[\begin{aligned}& \mathrm{f}: \mathrm{IN} \rightarrow \mathrm{IN} \\& \mathrm{f}(\mathrm{n})=(\mathrm{n}+5)^2, \mathrm{n} \in \mathrm{IN}\end{aligned}\](IN is the set of natural numbers). Then

Step-by-step Solution

A Mapping from IN to IN is defined as follows :
\[
\begin{aligned}
& \mathrm{f}: \mathrm{IN} \rightarrow \mathrm{IN} \\
& \mathrm{f}(\mathrm{n})=(\mathrm{n}+5)^2, \mathrm{n} \in \mathrm{IN}
\end{aligned}
\]
(IN is the set of natural numbers). Then