One method is to draw a triangle with the hypotenuse in quadrant II. The height of the triangle is 5, and the base is -2. The hypotenuse can be found using Pythagorean theorem:
c² = a² + b²
c² = (-2)² + (5)²
c = √29
Therefore, cos θ = -2/√29.
Another method is to use one of the Pythagorean identities.
