Trig Proof 1

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Taught by YourMathGal
  • Currently 4.0/5 Stars.
4201 views | 2 ratings
Part of video series
Meets NCTM Standards:
Errors in this video:

At 12 seconds into the video, cot(theta) is listed as cos(theta) / tan(theta), but it should say cot(theta) = cos(theta)/sin(theta).

Lesson Summary:

In this trigonometry lesson, viewers learn how to prove or verify trigonometric identities. The instructor presents three different trigonometric identities to be verified and walks through the steps to solve each one. The lesson emphasizes the importance of knowing fundamental identities and Pythagorean identities, as well as the ability to manipulate one side using identities until it looks like the other side. Viewers are encouraged to put everything in terms of cosines and sines and to be creative in their approach to solving identities.

Lesson Description:

Shows steps for proving (or verifying) Trigonometric Identities;

More free YouTube videos by Julie Harland are organized at

Questions answered by this video:
  • How do you verify / prove trig identities?
  • How do you prove that (cos(x)*sin^2(x) + cos^3(x))/sin(x) = cot(x)?
  • How do you prove that sin^2(x)/cos(x) = sec(x) - cos(x)?
  • How do you prove that tan(theta)*cos(theta) + csc(theta)*sin^2(theta) = 2*sin(theta)?
  • What are some fundamental trig identities that you need to know to prove trig formulas?
  • What are the Pythagorean identities for trigonometry?
  • Staff Review

    • Currently 4.0/5 Stars.
    This lesson shows how to verify / prove trig identities / formulas. Some tricks / techniques for transforming the left side of the trig identities to make them look like the right side are shown and explained. If you struggle with proving trig identities, this is a great lesson to watch.
  • darkhydrastar

    • Currently 4.0/5 Stars.
    Theres a small error in the fundamental identities at the beginning f the video. cotx is listed as cosx/tanx. Should be cosx/sinx. Excellent teacher though... Soothing voice and perfect pace I love that she uses color so effectively. Hopefully she adds more (conics?, trig transformstions?)