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Worked Examples · Example 2

Q.Evaluate lim⁡x→2x2−4x−2\displaystyle\lim_{x\to 2}\frac{x^2 - 4}{x - 2}.

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✓ Free question

Test substitution: at x=2x=2, numerator =22−4=0=2^2-4=0 and denominator =0=0, giving the indeterminate form 00\tfrac00 — transform before evaluating.

Factor and cancel (valid since x≠2x\neq2 throughout the limit process):

x2−4x−2=(x−2)(x+2)x−2=x+2.\frac{x^2-4}{x-2}=\frac{(x-2)(x+2)}{x-2}=x+2.

Now substitute: lim⁡x→2(x+2)=2+2=4\lim_{x\to2}(x+2)=2+2=4.

Verify (standard-limit route): x2−4x−2=x2−22x−2\dfrac{x^2-4}{x-2}=\dfrac{x^2-2^2}{x-2} matches xn−anx−a\dfrac{x^n-a^n}{x-a} with n=2,a=2n=2,a=2, giving n an−1=2⋅21=4n\,a^{n-1}=2\cdot2^{1}=4. Same answer.

✓Final answer

lim⁡x→2x2−4x−2=4\displaystyle\lim_{x\to 2}\frac{x^2-4}{x-2}=4.

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