Write p(x) = 21 + 24x + 6x2 in vertex form. p(x) = (x +__ )2 –

Vertex form is basically, just complete the square on the right side
group x terms together

factor out linear coefient (number in front of the higest power x, in this case x^2)

take 1/2 of the linear coefient and square it (4 is linear coefient so take 1/2 of it and square it (4/2=4, 4^2=4)), add positive and negative of it inside the parenthaees (so it equals 0)

factor perfect square trinomial
distribute (don't distribute or expand the squared term)