24cm
20cm
28cm
7cm
\(\frac{88}{7}\)
Correct answer is A
< B is the largest since the side facing it is the largest, i.e. (x + 4)cm
Cosine B = \(\frac{1}{5}\)
= 0.2 given
b2 - a2 + c2 - 2a Cos B
Cos B = \(\frac{a^2 + c^2 - b^2}{2ac}\)
\(\frac{1}{5}\) = \(\frac{x^2 + ?(x - 4)^2 - (x + 4)^2}{2x (x - 4)}\)
\(\frac{1}{5}\)= \(\frac{x(x - 16)}{2x(x - 4)}\)
\(\frac{1}{5}\) = \(\frac{x - 16}{2x - 8}\)
= 5(x - 16)
= 2x - 8
3x = 72
x = \(\frac{72}{3}\)
= 24