Let's assign the variable x to cosA. The expression then becomes x² - 5x + 6. To factorize this we need to find two numbers that have a sum of -5 and a product of 6; these numbers are -2 and -3 so the expression becomes (x - 2)(x - 3). Since we know that x = cosA the final answer is (cosA - 2)(cosA - 3).
