JAMB - Mathematics (1981 - No. 10)
What is the area between two concentric circles of diameters 26cm and 20cm?
100\(\pi\)
169\(\pi\)
69\(\pi\)
9\(\pi\)
269\(\pi\)
คำอธิบาย
Area of circle 1 with diameter 26cm:
\(\pi r^{2} = \pi \times (\frac{26}{2})^{2} \)
= \(169 \pi cm^{2}\)
Area of circle 2 with diameter 20 cm:
\(\pi R^{2} = \pi \times (\frac{20}{2})^{2}\)
= \(100 \pi cm^{2}\)
Area between the two circles = \((169 - 100) \pi cm^{2}\)
= \(69 \pi cm^{2}\)