In the figure shown, PT and PAB are the tangent and the secant drawn to a circle; PT = 12 cm and PA = 8 cm, then AB is equal to:
10 cm
By the tangent-secant theorem (power of a point), PT² = PA × PB. Substituting values gives 12² = 8 × PB, so PB = 18 cm. Since AB = PB − PA, AB = 18 − 8 = 10 cm. Note: the handwritten mark on this item in the source paper was faint and inconclusive, so this value follows the standard theorem.
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