The roots of the equation are , which you wrote as -6+-√6^2-4(1)(13)/2(1). As you know, in the standard order of operations division comes before subtraction, so your formula is . (In the text formula, it is also not clear where the square root ends.) And what about -6+-√16/2, which means or , but not ?
In any case, the main mistake is that the discriminant is negative.