JAMB - Mathematics (2001 - No. 42)
60o
100o
120o
30o
คำอธิบาย
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
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