The area of the region enclosed between two circles is 418 cm2. If the width of that region is 7 cm, find the radius of the bigger circle. दो वृत्त के मध्य स्थित भाग का क्षेत्रफल 418 सेमी2 है। यदि उस क्षेत्र की चौड़ाई 7 सेमी है, बड़े वृत्त की त्रिज्या ज्ञात कीजिए।

Let larger radius = R, smaller radius = r. Width of ring = R - r = 7 cm. Area of ring = π(R² - r²) = π(R - r)(R + r) = π × 7 × (R + r) = 418 cm². Therefore, R + r = 418/(7π) ≈ 19. Using R - r = 7 and R + r = 19: Adding equations: 2R = 26, so R = 13 cm. Option B (7 cm) is the ring width, not the radius. Option C (6 cm) would be the smaller radius. Option D (19 cm) is R + r, not R alone.