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Cosine Rule - Angles Step 1: To find an angle C, you need all 3 sides a, b & c. cos θ = 92 + 2 – 2 2 x 9 x Step 2: Sub the sides intothe formula, make sure youare subtracting the 'opposite'side to your missing angle. cos θ = 92 + 202 – 142 2 x 9 x 20 (Answer to 2 d.p., but keepall places on your screen) Step 3: Input into your calculator. = Step 4: Find θ by removingcos using cos–1. cos θ = 0.79..... θ = cos–1 0.79..... θ = (Answer correct to the nearest degree) o cos θ = 16.52 + 2 – 2 2 x 16.5 x Now, complete without the prompts. cos θ = 16.52 + 8.92 – 152 2 x 16.5 x 8.9 (Answer to 2 d.p., but keepall places on your screen) = cos θ = 0.43..... θ = (Answer correct to the nearest degree) o |