Review of Trig Identities

This weekend I am going to review with you all the information that we learned about identities. We learned this in trig. The identities are used to solve trig function equation. These are things like sin, cos, and tan. There are some identities that you need to know for this section.

Notes:

Reciprocal
• csc (theta)=1/sin (theta)
• sec (theta)=1/cos (theta)
• cot (theta)=1/tan (theta)
• tan (theta)=sin (theta)/ cos (theta)
• tan (theta)=cos (theta)/ sin (theta)

Pythagorean
• sin^2 (theta) + cos^2(theta) = 1
• 1 + tan^2 (theta) = sec^2 (theta)
• 1 + cot^2 (theta) = csc^2 (theta)

Cofunction
• sin(theta) = cos (90 degrees-theta)
• cos (theta) = sin (90 degrees-theta)
• tan(theta) = cot(90 degrees-theta)
• cot (theta) = tan (90 degrees-theta)
• sec (theta) = csc (90 degrees-theta)
• csc(theta) = sec (90 degrees-theta)

Example: Simplify: (sec^2x – tan^2x)/cos x
• You would use the identity that contains tan^2 and sec^2
• That would give you 1/cos x
• Your final answer would be secx


-Braxton-