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 =2(3)(5)9+25−49 = –21⇒ ∠C = 1200