so am I ... you don't complete the square of an expression like x<sup>2</sup> + 24, one with a quadratic term and a constant term.

if, however, you meant the expression to be x<sup>2</sup> + 24x ...

x<sup>2</sup> + 24x

divide the coefficient of the linear term in half ... square the result. Add and subtract the result from the expression ...

x<sup>2</sup> + 24x + 144 - 144

the first three terms are now a perfect square trinomial ... write it in factored form

(x + 12)<sup>2</sup> - 144

you're done.