Find the constant term that should be added to make the following expression a perfect-square trinomial.?

Question

x^2-18x

Answer 1

81

x^2 - 18x + 81
x^2 - 9x - 9x + 81
x(x - 9) - 9(x - 9)
(x - 9)(x - 9)

Answer 2

To find that constant term all you need to do is half the x-coefficient and then square it:

x^2 - 18x >>> 18/2 = 9 >>> 9^2 = 81

So 81 is what you need to add to make x^2 -18x a perfect square trinomial.

Answer 3

9

Answer 4

I'm taking a graduate math class and am just now appreciating how important it is to be able to 'complete the square'. You want to add an amount to make what you have a perfect square: x^2 + 7x +(7/2)^2 - (7/2)^2 (x+7/2)^2 - (7/2)^2 See how that works, It's a common technique to add zero in a form that gives you what you want.

Answer 5

81

Answer 6

shouldn't it be +81?