Target Exam

CUET

Subject

-- Applied Mathematics - Section B2

Chapter

Calculus

Question:

Determine whether the function $f(x) = \frac{1}{x}, x≥ 1$, is strictly increasing or decreasing for the stated values of x.

Options:

Strictly increasing for $x≥1$

Strictly decreasing for $x≥1$

Constant for $x≥1$

Neither increasing nor decreasing

Correct Answer:

Strictly increasing for $x≥1$

Explanation:

The correct answer is Option (1) → Strictly increasing for $x≥1$

Given $f(x) = \frac{1}{x}, x≥ 1⇒ f'(x) = 1-\frac{1}{x^2}$

Now $x≥1⇒x^2≥1⇒\frac{1}{x^2}≤1⇒0≤1-\frac{1}{x^2}⇒1-\frac{1}{x^2}≥0$

$∴f'(x) ≥ 0$ for $x ≥ 1$.

Note that $f'(x) = 0$ at $x = 1$ and $f'(x) > 0$ for all $x > 1$.

Therefore, f(x) is strictly increasing for $x ≥ 1$.