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Question
In triangle ABC, AB = AC = 15 cm and BC = 18 cm, find cos ∠ABC.
Solution
Consider the figure below :
In the isosceles ΔABC, AB = AC = 15cm and BC =18cm the perpendicular drawn from angle A to the side BC divides the side BC into two equal parts BD = DC = 9 cm
cos ∠ABC = `"base"/"hypotenuse" = "BD"/"AB" = (9)/(15) = (3)/(5)`
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