cos(a) = -(13/14) and represents the adjacent over the hypotenuse, or x/r with respect to the four quadrants thus making x negative - meaning the angle a is in the second or third quadrant.
Use the Pythagorean theorem to determine the opposite side length, or the y value.
y = √(14)2 - (13)2
y = √196-169
y = √27
y = 3√3
This represents the absolute value of y and note that y is positive in the second qaudrant and negative ib the third.
Tangent is opposite over the adjacent, or y/x. Since y can be positive or negative, tan(a) is either of two values:
tan(a) = y/x
tan(a) = (3√3)/(-13) = -3√3/13, or
tan(a) = -(3√3)/(-13) = 3√3/13
tan(a) = -3√3/13, or 3√3/13
