An astronomical unit (AU) is the average distance between Earth and the sun. One AU is equal to approximately 150,000,000 km. Astronomers also use light years to measure distance. A light year is approximately 9.5×1012 km.

Look at the figure below: triangle abc is a right triangle with angle abc equal to 90 degrees. the length of ac is 5 units and the length of ab is 4 units. d is a point above c. triangle adc is a right triangle with angle dac equal to 90 degrees and dc parallel to ab. what is the length, in units, of segment cd?