MathDB
Math Prize 2016 Problem 19

Source:

September 12, 2016
Math Prize for Girls

Problem Statement

In the coordinate plane, consider points A=(0,0)A = (0, 0), B=(11,0)B = (11, 0), and C=(18,0)C = (18, 0). Line A\ell_A has slope 1 and passes through AA. Line B\ell_B is vertical and passes through BB. Line C\ell_C has slope 1-1 and passes through CC. The three lines A\ell_A, B\ell_B, and C\ell_C begin rotating clockwise about points AA, BB, and CC, respectively. They rotate at the same angular rate. At any given time, the three lines form a triangle. Determine the largest possible area of such a triangle.