# C2 Trigonometric Identities - PowerPoint PPT Presentation

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C2 Trigonometric Identities. cos ²ø + sin ²ø = 1 So cos ²ø = 1 - sin ²ø And sin ²ø = 1 - cos ²ø. sin ø = tan ø cos ø. 1. Use this information to solve 2 cos ²ø – sinø – 1 = 0 for 0 ≤ ø ≤ 360. 2. Solve tan ø =4cosø for -180 ≤ ø ≤ 180.

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C2 Trigonometric Identities

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### C2 Trigonometric Identities

cos²ø + sin²ø = 1

So cos²ø = 1 - sin²ø

And sin²ø = 1 - cos²ø

sin ø = tan ø

cos ø

1. Use this information to solve

2 cos²ø – sinø – 1 = 0 for 0 ≤ ø ≤ 360

2. Solve

tanø =4cosø for -180 ≤ ø ≤ 180

2 cos²ø – sinø – 1 = 0 for 0 ≤ ø ≤ 360

Cos²ø = 1 - sin²ø

2(1 - sin²ø) – sinø – 1=0

2 - 2sin²ø – sinø – 1=0

2sin²ø + sinø – 1=0

Factorise (2sinø - 1)(sinø + 1)=0

sinø = ½ or sinø = -1

ø = 30º, 150º or 270º

Solve tanø =4cosø for -180 ≤ ø ≤ 180

sin ø = 4cosø

cos ø

sinø = 4cos²ø

sinø = 4(1-sin²ø)

sinø = 4 - 4sin²ø

4sin²ø – sinø – 4 = 0 (use formula to solve)

sinø = 0.8828 or sinø = -1.1328 (no solutions)

ø = 62.0º, 118º