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If f(4) = 4, f '(4) = 1, then \(\displaystyle\lim_{x \rightarrow 4} \dfrac{2- \sqrt{f(x)}}{2-\sqrt x}\) is equal to:
1. -2
2. 2
3. 1
4. -1

1 Answer

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Best answer
Correct Answer - Option 3 : 1

Concept: 

If f(x)/g(x) is in the from 0/0 or ∞/∞ Where x = a plugs in , then : 

\(lim_{x→a}\) f(x)/g(x) =  \(lim_{x→a}\) f'(x)/g'(X)

Calculation: 

Given: 

f(4) = 4, f '(4) = 1, then \(\displaystyle\lim_{x \rightarrow 4} \dfrac{2- \sqrt{f(x)}}{2-\sqrt x}\) from(0/0)

Now by L-Hospital Rule , 

⇒ \(lim_{x→4}\) \(\frac{0-\frac{1}{2\sqrt{f(n)}}×f'(n)}{0-\frac{1}{2\sqrt{n}}}\)

⇒ \(lim_{x→4}\) \(\frac{f'(x)}{\sqrt{f(x)}}×\sqrt{x}\)

⇒ \(\frac{f'(4)}{\sqrt{f(4)}}×\sqrt{4}\)

⇒ \(\frac{1×2}{\sqrt{4}}\)

1

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