find the length XZ in the triangle - JAMB Mathematics 1999 Question

A
\(\sqrt{7m}\)
B
\(\sqrt{6m}\)
C
\(\sqrt{5m}\)
D
\(\sqrt{3m}\)
correct option: a
xz2 = xy2 + yx2 - 2(xy) (yz) cos 120o
= 22 + 12 - 2(2) (1) cos 1202
= 4 + 1 - 4x - cos 60 = 5 - 4x - (\frac{1}{2})
5 + 2 = 7
xz = (\sqrt{7})m
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