Answer:
Starting with the left side of the equation:
cos² a + cos² a cot² a
We can simplify the left side by using the identity cot² a = 1/tan² a
cos² a + cos² a * (1/tan² a)
We can simplify further by using the identity tan² a = (1/cos² a) - 1
cos² a + (1 - cos² a)
Now we have the left side of the equation equals to 1 which is the right side of the equation.
Explanation:
see above