<u>Explanation</u> We are going to take angle ∅ to be at the origin (point (0,0)). The point at (-2, -3) means, 2 units to the left (negative side of x-axis) and 3 units downwards (negative side of y-xis). This will make a right triangle with a hypotenuse of √(2²+3²) = √13
The angle ∅ is in the 3rd quadrant where cosine is negative.