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Question
From the given figure, find the values of cos C
Solution
In the right ΔABD,
AD2 = AB2 – BD2
= 132 – 52
= 169 – 25
= 144
AD = `sqrt(144)`
= 12
In the right ΔADC,
AC2 = AD2 + DC2
= 122 + 162
= 144 + 256
= 400
AC = `sqrt(400)`
= 20
cos C = `"adjacent side"/"hypotenuse" = "CD"/"AC" = 16/20 = 4/5`
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