6 = x² - 10x. Re-write it:
x² - 10 - 6 = 0. This is a quadratic equation (ax²+bx+c=0) and the solutions are given by the following formula:
x' = [-b + √(b²-4ac)]/2a and x" = [-b - √(b²-4ac)]/2a
(for your info a =1, b= -10, c= - 6). Plug in the related values and you'll find:
x' =5+√31 and x" = 5-√31
