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The sides of a triangle are(x + 4)cm, xcm and (x - 4)cm, res...

The sides of a triangle are(x + 4)cm, xcm and (x - 4)cm, respectively If the cosine of the largest angle is 15, find the value of x

A.

24cm

B.

20cm

C.

28cm

D.

7cm

E.

887

Correct answer is A

< B is the largest since the side facing it is the largest, i.e. (x + 4)cm

Cosine B = 15

= 0.2 given

b2 - a2 + c2 - 2a Cos B

Cos B = a2+c2b22ac

15 = x2+?(x4)2(x+4)22x(x4)

15= x(x16)2x(x4)

15 = x162x8

= 5(x - 16)

= 2x - 8

3x = 72

x = 723

= 24