6.5 The Cosine Ratio B Hypotenuse Opposite C Adjacent A The cosine ratio for acute angle A, is the ratio of the length of the adjacent side (to angle A) over the length of the hypotenuse. adjacent __________ cos A = hypotenuse 1 Example 1 Use the cosine ratio to calculate the length of t. R t S s=15 cm r 40o T 2 Example 2 Use the cosine ratio to calculate the measure of B. B a C c = 10 cm b = 8 cm A 3 Example 3 Application A ladder leans against a vertical wall and makes an angle of 65o with the ground. The foot of the ladder is 2 m from the base of the wall. Calculate the length of the ladder, to the nearest tenth of a metre. 4

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