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Perhaps they just want you to write the term tan^2x-sec^2x in terms of sines and cosines. If so, they should have said so.
simplify and write the trigonometric equation in terms of sine and cosine.
tan^2x-sec^2x
2 answers
from the main Pythagorean Identity we know
tan^2 x + 1 = sec^2 x
so tan^2x-sec^2x = tan^2 x - (tan^2 x + 1)
= -1
tan^2 x + 1 = sec^2 x
so tan^2x-sec^2x = tan^2 x - (tan^2 x + 1)
= -1