Work Step by Step
Use the identity on page 655, $\tan^2x+1=\sec^2x$, and subtract $1$ from both sides: $\tan^2x=\sec^2x-1$ So $\sec^2 x-1=\tan^2 x$.
You can help us out by revising, improving and updating this answer.Update this answer
After you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.