Can you please explain Test 3 Section 4 #23?

Yep! The key to getting this one is recognizing that when they tell you that , they’re telling you that . That’s just a little trig fact you should keep in mind when you’re taking the SAT. It can be derived pretty easily—just picture any right triangle with acute angles measuring and :

Of course, since it’s a right triangle, . And if you do your SOH-CAH-TOA, you’ll see that and .

Anyway, back to the question. Once we recognize that , the rest is just substitution.