91Ó°ÊÓ

Two tangents to a circle are at right angles with each other. A point on the smaller arc between the two points of tangency is \(4(1 / 2)\) in. from one tangent line and 4 in. from the other. Find the radius of the circle.

Two parallel tangents are drawn to a circle whose center is O. A third tangent is drawn intersecting the first two at \(\mathrm{A}\) and \(\mathrm{B}\). Prove that the circle constructed with diameter \(\mathrm{AB}\) passes through \(\mathrm{O}\).