Question

If a=2,b=3,c=5, then find cosC.

Answer 1

Answer:

5 is the answer

please give me thanks

Answer 2

In a Triangle ABC,

If AB = c, BC = a, AC = b

By cosine rule,

c² = a² + b² - 2abcosC

2abcosC= a² + b² - c²

$cosC = \frac{ {a}^{2} + {b}^{2} - {c}^{2} }{2ab}$

Given

a = 2,

b = 3,

c = 5

Now,

$cosC = \frac{ {a}^{2} + {b}^{2} - {c}^{2} }{2ab} \\ \\ cosC = \frac{ {2}^{2} + {3}^{2} - {5}^{2} }{2(2)(3)} \\ \\ cosC = \frac{4 + 9 - 25}{12} \\ \\ cosC = \frac{13 - 25 }{12} \\ \\ cosC = \frac{ - 12}{12} \\ \\ cosC = - 1$

Therefore, cosC = - 1