III. 16 to 19.
176. Shew that two tangents can be drawn to a circle from a given external point, and that they are of equal length.
177. Draw parallel to a given straight line a straight line to touch a given circle.
178. Draw perpendicular to a given straight line a straight line to touch a given circle.
179. In the diameter of a circle produced, determine a point so that the tangent drawn from it to the circumference shall be of given length.
180. Two circles have the same centre: shew that all chords of the outer circle which touch the inner circle are equal.
181. Through a given point draw a straight line so that the part intercepted by the circumference of a given circle shall be equal to a given straight line not greater than the diameter.
182. Two tangents are drawn to a circle at the opposite extremities of a diameter, and cut off from a third tangent a portion AB: if C be the centre of the circle shew that ACB is a right angle.
183. Describe a circle that shall have a given radius and touch a given circle and a given straight line.
184. A circle is drawn to touch a given circle and a given straight line. Shew that the points of contact are always in the same straight line with a fixed point in the circumference of the given circle.
185. Draw a straight line to touch each of two given circles
186. Draw a straight line to touch one given circle so that the part of it contained by another given circle shall be equal to a given straight line not greater than the diameter of the latter circle.
187. Draw a straight line cutting two given circles so that the chords intercepted within the circles shall have given lengths,
188. A quadrilateral is described so that its sides touch a circle: shew that two of its sides are together equal to the other two sides.
189. Shew that no parallelogram can be described about a circle except a rhombus.
