Question #50ca2 Trigonometry Trigonometric Identities and Equations Proving Identities 1 Answer Andrea S. Mar 27, 2017 cos theta/(1-sintheta) = sec theta + tan theta Explanation: Start from the first member: cos theta/(1-sintheta) multiply and divide by (1+sin theta): cos theta/(1-sintheta) = cos theta/(1-sintheta) (1+sin theta)/(1+sin theta) cos theta/(1-sintheta) = cos theta(1+sintheta)/ (1-sin^2 theta) cos theta/(1-sintheta) = cos theta(1+sintheta)/ cos^2 theta cos theta/(1-sintheta) = (1+sintheta)/ cos theta cos theta/(1-sintheta) = 1/cos theta +sintheta/ cos theta cos theta/(1-sintheta) = sec theta + tan theta Answer link Related questions What does it mean to prove a trigonometric identity? How do you prove \csc \theta \times \tan \theta = \sec \theta? How do you prove (1-\cos^2 x)(1+\cot^2 x) = 1? How do you show that 2 \sin x \cos x = \sin 2x? is true for (5pi)/6? How do you prove that sec xcot x = csc x? How do you prove that cos 2x(1 + tan 2x) = 1? How do you prove that (2sinx)/[secx(cos4x-sin4x)]=tan2x? How do you verify the identity: -cotx =(sin3x+sinx)/(cos3x-cosx)? How do you prove that (tanx+cosx)/(1+sinx)=secx? How do you prove the identity (sinx - cosx)/(sinx + cosx) = (2sin^2x-1)/(1+2sinxcosx)? See all questions in Proving Identities Impact of this question 1490 views around the world You can reuse this answer Creative Commons License