Question

If the length of the sides of triangle are $3,5$ and $7$ and the largest angle of the triangle is

• A. $\frac{\pi }{2}$
• B. $\frac{5\pi }{6}$
• C. $\frac{2\pi }{3}$
• D. $\frac{3\pi }{4}$

Answer 1

The correct option is A $\frac{\pi }{2}$

since the largest angle is opposite of largest side,

$cosC=\frac{3^2+5^2-7^2}{2\left(3\right)\left(5\right)}=\frac{-15}{30}$

$=\frac{-1}{2}$

$C=\frac{2\pi }{3}$