Limit, continuity, derivative, and integral

Problem

For x≠1x\ne1, let f(x)=(x2−1)/(x−1)f(x)=(x^2-1)/(x-1). Choose f(1)f(1) so that ff is continuous. For that continuous extension, find f′(1)f'(1) and ∫02f(x) dx\int_0^2 f(x)\,dx.

Reveal answer or reference solution

For x≠1x\ne1, f(x)=x+1f(x)=x+1, so lim⁡x→1f(x)=2\lim_{x\to1}f(x)=2. Set f(1)=2f(1)=2. The extended function is x+1x+1 everywhere, hence f′(1)=1f'(1)=1 and

∫02(x+1) dx=[x22+x]02=4\int_0^2(x+1)\,dx=\left[\frac{x^2}{2}+x\right]_0^2=4
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