Compute using Trig Identities 1

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Taught by YourMathGal
  • Currently 4.0/5 Stars.
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Part of video series
Meets NCTM Standards:
Lesson Summary:

In this lesson, Julie Harland teaches us how to use trig identities to make computations. She walks us through a problem where we're given the cosine of 2A and we're trying to find the cosine, sine, and tangent of A. Julie shows us how to use the formula for the cosine of 2A to find the cosine of A and then walks us through different methods for finding the sine of A. She reminds us to be careful of signs and offers a variety of ways to approach similar problems.

Lesson Description:

Using Trig Identities to make computations.

More free YouTube videos by Julie Harland are organized at

Questions answered by this video:
  • How do you make computations using trig identities?
  • If cos(2A) = 1/3 and 360 < 2A < 450, what are cosA, sinA, and tanA?
  • How do you find cosA, sinA, and tanA if you know cos(2A)?
  • Staff Review

    • Currently 4.0/5 Stars.
    This lesson shows how to compute cos, sin, and tan of an angle if you know the value of cos of twice the angle. All steps involved in making the computations are shown and explained very clearly in this lesson. Check out the next lessons in this series for more example problems.