Use the inverse of the function y = x2 − 18x to find the unknown values. y=+/= square root of bx+c+d

y = x2 - 18x

 We look for the inverse of the function.
 To do this, let's determine the value of x:
 y = x2 - 18x
 y = (x + (-18/2)) ^ 2 - ((-18) ^ 2/4) + 0
 y = (x - 9) ^ 2 - 81
 y + 81 = (x - 9) ^ 2
 +/- root (y + 81) = (x - 9)
 +/- root (y + 81) + 9 = x
 We return the change:
 f (x) ^ - 1 = +/- root (x + 81) + 9
 Therefore, the values sought are:
 b = 1
 c = 81
 d = 9
 Answer: 
 f (x) ^ - 1 = +/- root (x + 81) + 9 
 b = 1
 c = 81
 d = 9