Mathematics

Problem

For the circle

x^2 + y^2 = a^2

, the slope of the tangent at a point

(x_1, y_1)

on the circle is a)

\dfrac{x_1}{y_1}

-\dfrac{y_1}{x_1}

-\dfrac{x_1}{y_1}

\dfrac{y_1}{x_1}