Deriving the Law of Cosines

Which of the following formulas shows the Law of Cosines?

• c² = a² + b² - 4ac + cosA
• c² = a² - b² - 2abcosC
• c² = a² + b² - 2abcosC
• (cos A)/a = (cos B)/b

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CCSS.HSG.SRT.D.10

CCSS.HSG.SRT.D.11

If three sides of a triangle are given, the Law of ____ is used to solve the triangle.

• Cosines
• Sines
• Tangent
• Cosecents

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CCSS.HSG.SRT.D.10

CCSS.HSG.SRT.D.11

Which Law would you use?

• Law of Sines
• Law of Cosines
• Law of the Jungle
• Law of Gravity

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CCSS.HSG.SRT.D.10

CCSS.HSG.SRT.D.11

Find XZ

• 16.004 meters
• 544.165 meters
• 34.7 meters
• 1204.165 meters

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CCSS.HSG.SRT.D.10

CCSS.HSG.SRT.D.11

4. Name the smallest angle in this triangle.

• ∠A

• ∠B

• ∠C

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CCSS.HSG.CO.C.10

Which Law would you use?

• Law of Sines
• Law of Cosines
• Law of the Jungle
• Law of Gravity

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CCSS.HSG.SRT.D.10

CCSS.HSG.SRT.D.11

Find angle Z

• 20.15°

• 71.23°

• 51.06°

• 57.71°

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CCSS.HSG.SRT.D.10

CCSS.HSG.SRT.D.11

Use Law of Cosines to find angle T

• 62.2 degrees
• 53.1 degrees
• 59.5 degrees
• 64.7 degrees

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CCSS.HSG.SRT.D.10

CCSS.HSG.SRT.D.11

To approximate the length of a marsh, a surveyor walks 425 meters from point A to point B. Then the surveyor turns 65º and walks 300 meters to point C. Approximate the length AC of the marsh.

• 250

• 615

• :)

• Not me

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CCSS.HSG.SRT.D.10

CCSS.HSG.SRT.D.11