2x^2 + 42x + 260 = 6x
2x^2 + 42x - 6x + 260 = 0
2x^2 + 36x + 260 = 0 divide through by 2
x^2 + 18x + 130 = 0
take 1/2 of 18 = 9,,,,square it = 81....add it and subtract it
x^2 + 18x + 81 + 130 - 81 = 0 factor the first three terms, simplify the rest
(x + 9)^2 + 51 = 0
(x + 9)^2 = -51