JAMB - Mathematics (2001 - No. 42)

Find the value of \(\theta\) in the diagram
60o
100o
120o
30o

Explanation

Using cosine formula (t\(\sqrt{3}\))2 = t2 + t2 - 2t2 cos\(\theta\)

3t2 = 2t2 - 2t2 cos\(\theta\) = 2t2(1 - cos\(\theta\))

1 - cos\(\theta\) = \(\frac{3t^2}{2t^2}\) = \(\frac{3}{2}\)

cos = 1 - \(\frac{3}{2} = -\frac{1}{2}\)

\(\theta\) = cos-1(-\(\frac{1}{2}\)) = 120o and 240o

N.B 0 \(\geq\) \(\theta\) 360

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