Rectangle has , and . The rectangle is curled without overlapping into a cylinder so that sides and touch each other. In other words, touches and touches . The shortest distance from to through the inside of the cylinder can be written in the form where and are positive integers. What is the smallest possible value of ?
Solution
When the cylinder is created, and touch and and touch. This means that is vertical and so is perpendicular to the plane of the circular base of the cylinder. This means that is right-angled at . By the Pythagorean Theorem, . Note that equals the height of the rectangle, which is 3 (the length of ) and that is now measured through the cylinder, not along the line segment . Let be the centre of the circular base of the cylinder. In the original rectangle, and , which means that . This means that is one-quarter of the way around the circumference of the circular base from back to . As a result, , since is one-quarter of a complete circular angle. Thus, is right-angled at . By the Pythagorean Theorem, . Since and are radii of the circular base, then and so . Since the circumference of the circular base is 4 (the original length of ), then if the radius of the base is , we have and so . Since , then . This means that and so . Since the coefficient of in the denominator is 1, it is not possible to 'reduce' the values of and any further, and so , and , which gives .