What number must you add to complete the square x2 plus 26x equals 68?

x2+26x = 68

x2+26x-68 = 0

(x+13)2-68 = 0

(x+13)2-169-68 = 0

x+13 = +/- the square root of 237

x = -13 +/- the square root of 237