The graph of $y=x^2+2x-15$ intersects the $x$-axis at points $A$ and $C$ and the $y$-axis at point $B$. What is $\tan(\angle ABC)$? $\textbf{(A) }\frac{1}{7} \qquad$ $ \textbf{(B) }\frac{1}{4} \qquad$ $ \textbf{(C) }\frac{3}{7} \qquad$ $ \textbf{(D) }\frac{1}{2} \qquad$ $ \textbf{(E) }\frac{4}{7}$
Solution
$x^2+2x-15=0\Rightarrow x=3$ or $x=-5$, so $A=(-5,0),C=(3,0),B=(0,-15)$.
