The problem asks to evaluate the limit $\lim_{x \to \infty} (\sqrt{x^2+x} - \sqrt{x^2-1})$.

AnalysisLimitsCalculusRationalizationSquare Roots
2025/5/21

1. Problem Description

The problem asks to evaluate the limit
limx(x2+xx21)\lim_{x \to \infty} (\sqrt{x^2+x} - \sqrt{x^2-1}).

2. Solution Steps

We can rewrite the expression by multiplying by the conjugate and dividing by the same conjugate:
x2+xx21=(x2+xx21)x2+x+x21x2+x+x21\sqrt{x^2+x} - \sqrt{x^2-1} = (\sqrt{x^2+x} - \sqrt{x^2-1}) \cdot \frac{\sqrt{x^2+x} + \sqrt{x^2-1}}{\sqrt{x^2+x} + \sqrt{x^2-1}}
=(x2+x)(x21)x2+x+x21= \frac{(x^2+x) - (x^2-1)}{\sqrt{x^2+x} + \sqrt{x^2-1}}
=x+1x2+x+x21= \frac{x+1}{\sqrt{x^2+x} + \sqrt{x^2-1}}
Now, we divide both the numerator and the denominator by xx. Since xx \to \infty, we can assume x>0x>0, so x2=x\sqrt{x^2} = x.
x+1x2+x+x21=x+1xx2+xx+x21x=1+1xx2+xx2+x21x2\frac{x+1}{\sqrt{x^2+x} + \sqrt{x^2-1}} = \frac{\frac{x+1}{x}}{\frac{\sqrt{x^2+x}}{x} + \frac{\sqrt{x^2-1}}{x}} = \frac{1+\frac{1}{x}}{\sqrt{\frac{x^2+x}{x^2}} + \sqrt{\frac{x^2-1}{x^2}}}
=1+1x1+1x+11x2= \frac{1+\frac{1}{x}}{\sqrt{1+\frac{1}{x}} + \sqrt{1-\frac{1}{x^2}}}
Now we take the limit as xx \to \infty.
limx1+1x1+1x+11x2=1+01+0+10=11+1=11+1=12\lim_{x \to \infty} \frac{1+\frac{1}{x}}{\sqrt{1+\frac{1}{x}} + \sqrt{1-\frac{1}{x^2}}} = \frac{1+0}{\sqrt{1+0} + \sqrt{1-0}} = \frac{1}{\sqrt{1} + \sqrt{1}} = \frac{1}{1+1} = \frac{1}{2}

3. Final Answer

1/2

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