1 / 12

Law of Cosines

Law of Cosines. No longer dealing with Right Triangles!. Law of cosines is a tool to solve triangles that are not right-angled (oblique triangles) We need to know three things in order to use the law: Either all 3 sides , or two sides of a triangle and their included angle. If we know:

adlai
Download Presentation

Law of Cosines

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Law of Cosines

  2. No longer dealing with Right Triangles! • Law of cosines is a tool to solve triangles that are not right-angled (oblique triangles) • We need to know three things in order to use the law: Either all 3 sides, or two sides of a triangle and their included angle

  3. If we know: a, b, and θ We can find side c. c a θ b

  4. The Law of Cosines • For any • Notice the side on the left of the = sign is the same as the angle you are taking cos of.

  5. Example 1 • Use the Law of Cosines to find side length a.

  6. Example 1 Cont… Since we are given the angle A, and we are looking for side a, we will use original plug in values simplify * a Square root

  7. You try!

  8. Use the law in a different way: • Find angle T.

  9. Solution • 81 = 245 – 196 • – 164 = – 196 • .8367….. = • T = 33.2°

  10. Apply Law to more difficult example: In parallelogram BCDE, angle C is 65°. How long is each diagonal to one decimal place?

  11. Solution CD =6.4 BE = 9.4 Trick: Recall, Angle c and angle E sum to 180, so we can determine angle E = 115°

  12. Homework • Law of Cosines Page 511 • Problems 1,3,7

More Related