Answer:
fourth option
Step-by-step explanation:
Using the trigonometric identity
cos²x + sin²x = 1
Divide all terms by cos²x
[tex]\frac{cos^2x}{cos^2x}[/tex] + [tex]\frac{sin^2x}{cos^2x}[/tex] = [tex]\frac{1}{cos^2x}[/tex] which gives
1 + tan²x = sec²x
