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Question

Question: If the lengths of the sides of a triangle are 3, 5, 7, then the largest angle of the triangle is...

If the lengths of the sides of a triangle are 3, 5, 7, then the

largest angle of the triangle is

A

π/2

B

5π/6

C

2π/3

D

3π/4

Answer

2π/3

Explanation

Solution

a = 3, b = 5, c = 7

cos C =

⇒ cos C =9+25492(3)(5)\frac { 9 + 25 - 49 } { 2 ( 3 ) ( 5 ) } = –12\frac { 1 } { 2 }⇒ ∠C = 1200