## A circle has an equation of x^2 + y^2 + 2cy = 0. Find the value of c when the length of the tangent from (5, 4) to the circle is equal to one.

**Problem**

A circle has an equation of $x^2 + y^2 + 2cy = 0$. Find the value of $c$ when the length of the tangent from (5, 4) to the circle is equal to one.

A. 5 | C. 3 |

B. -3 | D. -5 |