Pythagorean Identity

CONCEPTS

Pythagorean Identity

• cos² θ + sin² θ = 1

• This can be used on any triangle (not just right triangles)

PRACTICE PROBLEMS

Question 1 Given sin² θ = 4/13, what is cos² θ

-- Answer -- 9/13

sin² θ + cos² θ = 1, 4/13 + cos² θ = 1

cos² θ = 9/13

Question 2 Given sin² (8x) = 4/13, what is cos² (8x)?

-- Answer -- 9/13

θ = 8x and sin² (8x) = 4/13

cos² θ + sin² θ = 1=> cos² θ + 4/13 = 1 => cos² θ = 1 - 4/13 = 9/13

ACT PRACTICE PROBLEMS

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