LISP PROGRAMMING

Please explain each step with a comment

Write a function roots which takes three numbers, a, b, and c and uses the quadratic formula to compute -b +62 - 4ac solutions to ax2 + bx + c = 0. Use the formula 2a to compute the roots and return them as a list. Assume that a is not 0 and that b2 2 4ac. Return the roots as a list with the first element being the + result and the second being the - result. As a special case, if the two roots are the same, return a list containing just the one root. For example, (roots -2 7 15) returns (list -1.5 5) (roots 1 -2 1) returns (list 1)