Question

Which of the following is NOT a Trig identity?

Answer 1

Option C. is a trigonometric identity
sin^2 A + cos^2 A = 1

Dividing by cos^2 A we get:
sin^2 A / cos^2 A + cos^2 A / cos^2 A = 1 / cos^2 A
tan^2 A + 1 = sec^2 A this is Option B and Option D.

Answer: Option A