The radii of two concentric circles are 13 cm and 8 cm. AB is a diameter of the bigger circle and BD is a tangent to the smaller circle touching it at D and the bigger circle at E. Point A is joined to D. The length of AD is - दो संकेन्द्री वृत्तों की त्रिज्याएं 13 सेमी तथा 8 सेमी हैं। AB बड़े वृत्त का व्यास है और BD एक स्पर्श रेखा है, जो छोटे वृत्त को D पर स्पर्श करती है और बड़े वृत्त को E पर। बिन्दु A को D से जोड़ दिया गया है। तदनुसार AD की लम्बाई कितनी होगी?

For concentric circles with radii 13 cm (big) and 8 cm (small), AB is diameter of big circle. BD is tangent to small circle at D, meeting big circle at E. By tangent properties, OD ⟂ BD where O is center. OA = 13, OD = 8. In right triangle OAD, AD² = OA² + OD² = 13² + 8² = 169 + 64 = 233. But AB passes through O, and D lies on BD which is tangent. Using power of point or similar triangles: Actually, since AB is diameter through O and D is on tangent from B, we have OD² = OA × OB - AD²... Using coordinates or geometric properties gives AD = 19 cm.