JAMB - Mathematics (1981 - No. 17)
An isosceles triangle of sides 13cm, 13cm, 10cm is inscribed in a circle. What is the radius of the circle?
7cm
12cm
8cm
7cm
69cm
Giải thích
In \(\Delta DAC, \stackrel\frown{DAC} = \theta\)
\(\sin \theta = \frac{5}{13}\)
\(\theta = 22.6°\)
\(< DOC = 22.6° \times 2 = 45.2°\)
\(\sin 45.2 = \frac{5}{r} \implies r = \frac{5}{\sin 45.2}\)
\(r = 7.046cm\)
= \(7\frac{1}{24} cm\)