math problem for _|x|_

1/(x-7)^2 = a
1 = a* (x-7)^2 //multiply both sides by (x-7)^2

1/a = (x-7)^2 //divide both sides by a

\/(1/a) = x-7 //take square root on both sides (\/ means square root :) )

\/(1/a) - 7 = x// subtract 7 from both sides

Bingo!

x = \/(1/a) - 7

or x = 1/\/a - 7