In given figure, a circle with centre O is inscribed in a quadrilateral ABCD such that, it touches the sides BC, AB, AD and CD at points P, Q, R and S respectively. If AB = 29 cm, AD = 23 cm, ∠B = 90∘ and DS = 5 cm, then the radius of the circle is ___ cm.
11
Let radius of the circle = r
We know that the lengths of the tangents drawn from an external point to a circle are equal.
BP = BQ = r ...... (OQBPis a square)
AQ = 29 - r
DS = DR = 5 cm
∴ AR = AD – DR = 23 cm – 5 cm = 18 cm
But, AQ = AR
29 - r = 18
r = 11 cm