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About Steve Holleran
Expertise
I can help with all math questions from basic math to Calculus. Whether it`s consumer questions, or questions from high school or college students, I have probably dealt with it at some time in my career.

Experience
33 years teaching experience in NJ public schools

Education/Credentials
B.S. Mathematics : Wake Forest University 1972 M.S. Mathematics : Monmouth University 1981

You are here: Experts > Science > Mathematics > Advanced Math > Trig Identity (Proving equal on 1 side)

Topic: Advanced Math

Expert: Steve Holleran
Date: 5/8/2008
Subject: Trig Identity (Proving equal on 1 side)

Question
(tanA + cotA)(secA - cosA) = secAtanA

Answer
Hi Rachel,

Okay, we're working on the left side:

(tan A + cot A)(sec A - cos A)

= tan A sec A - tan A cos A + cot A sec A - cot A cos A

= tan A sec A - (sin A/cos A)cos A + (cos A/sin A)(1/cos A)
- (cos A/sin A)cos A

= tan A sec A - sin A + (1/sin A) - (cos^2 A /sin A)

= tan A sec A - sin A + ((1-cos^2 A)/sin A)

= tan A sec A - sin A + (sin^2 A / sin A)

= tan A sec A - sin A + sin A = tan A sec A

Hope this helps.

Steve

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