# In ∆ABC, if a = 13, b = 14, c = 15, then find the value of cos B - Mathematics and Statistics

Sum

In ∆ABC, if a = 13, b = 14, c = 15, then find the value of cos B

#### Solution

By cosine rule, we have

cos B = ("c"^2 +"a"^2 - "b"^2)/(2"ca")

∴ cos B = (15^2 + 13^2 - 14^2)/(2 xx 15 xx 13)

= (225 + 169 - 196)/390

= 198/390

∴ cos B = 33/65

Concept: Solutions of Triangle
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