## University Calculus: Early Transcendentals (3rd Edition)

$$y=f(x)=x^{3/5}$$ a) The graph is enclosed below. From the introduction, we can guess that the graph appears to have vertical tangent at the origin. We will test this in part b). b) The graph of $f(x)$ has a vertical tangent at $x$ when 1) $f$ is continuous at $x$ 2) $$f′(x)=\lim_{h\to0}\frac{f(x+h)−f(x)}{h}=\pm\infty$$ Considering $f'(0)$, we have: $$f′(0)=\lim_{h\to0}\frac{f(h)−f(0)}{h}=\lim_{h\to0}\frac{h^{3/5}-0^{3/5}}{h}=\lim_{h\to0}\frac{h^{3/5}}{h}$$ $$f'(0)=\lim_{h\to0}\frac{1}{h^{2/5}}$$ As $h\to0^+$ or $h\to0^-$, $h^{2/5}$ always approaches $0^+$. Therefore, $$f'(0)=\lim_{h\to0}\frac{1}{h^{2/5}}=\infty$$ This means $f(x)$ has a vertical tangent at the origin as predicted.