So first we need to make sure we know the trig identities to solve this problem.
Here we only have two legs of the triangle, so we will need to use the Pythagorean Theorem a² + b² = c² to solve for the missing leg, the hypotenuse in this case.
Solving for the hypotenuse, c, we get
Here a = 20 and b = 21, so plugging in these values to the equation we get:
Now we can use the trig identities to figure out the missing values for the problem