Consider the following geometric sequence -5, 10, -20, if the recursive formula for the sequence above expressed in the form a(n)=b*c^n-1, determine the value of b and c.

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?