Question 431928
r^2 + 6r - 8 = 0
r^2 + 6r = 8 
take 1/2 of 6, square the result and add to both sides:
r^2 + 6r + 9 = 8 + 9
r^2 + 6r + 9 = 17
(r+3)(r+3) = 17
(r+3)^2 = 17
r+3 = {{{sqrt(17)}}}
r = {{{sqrt(17) - 3}}}