Question 1 • Precalculus
Start with the Pythagorean identity, cos² x + sin² x = 1. Divide every term by cos² x to get cos² x/cos² x + sin² x/cos² x = 1/cos² x, which is choice D. Since cos² x/cos² x = 1, sin² x/cos² x = tan² x, and 1/cos² x = sec² x, this gives 1 + tan² x = sec² x.
AI-written and checked against the verified answer.