Correct Answer: Option A

Explanation

< 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

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