This is probably going to be a very silly question but I feel very confused.
The math problem is,
Rename x[sup:18fmecll]2[/sup:18fmecll] - 9x as an expression involving a perfect square trinomial.
So I did,
x[sup:18fmecll]2[/sup:18fmecll] -9x =
x[sup:18fmecll]2[/sup:18fmecll] -9x + (-9/2)^2 - (-9/2)^2
(x - 9/2)[sup:18fmecll]2[/sup:18fmecll] - (-9/2)[sup:18fmecll]2[/sup:18fmecll]
And this is where I hit the snag. The answer is (x - 9/2)[sup:18fmecll]2[/sup:18fmecll] - 81/4.
Which does makes sense if it is (-9/2)[sup:18fmecll]2[/sup:18fmecll], since (-9)[sup:18fmecll]2[/sup:18fmecll] is 81, but what I don't understand is why the negative would be with the 9 in the Parentheses. I mean when I wrote out the problem above I put in it, just so I could keep track of all the negatives. But how does one know it's supposed to be there.
I have this vague idea of almost being able to get it, I mean it is negative 9 over two, and therefore it would make sense if you times the fraction by the power of two that that would probably include the negative. But I keep writing out this post, thinking I get it, deleting the whole thing and then having second doubts and writing the whole thing out again. I just want to make certain that I understand. I have the lot of trouble in completing the square problems with negatives and positives, I keep getting quite muddled up. *sighs*.
The math problem is,
Rename x[sup:18fmecll]2[/sup:18fmecll] - 9x as an expression involving a perfect square trinomial.
So I did,
x[sup:18fmecll]2[/sup:18fmecll] -9x =
x[sup:18fmecll]2[/sup:18fmecll] -9x + (-9/2)^2 - (-9/2)^2
(x - 9/2)[sup:18fmecll]2[/sup:18fmecll] - (-9/2)[sup:18fmecll]2[/sup:18fmecll]
And this is where I hit the snag. The answer is (x - 9/2)[sup:18fmecll]2[/sup:18fmecll] - 81/4.
Which does makes sense if it is (-9/2)[sup:18fmecll]2[/sup:18fmecll], since (-9)[sup:18fmecll]2[/sup:18fmecll] is 81, but what I don't understand is why the negative would be with the 9 in the Parentheses. I mean when I wrote out the problem above I put in it, just so I could keep track of all the negatives. But how does one know it's supposed to be there.
I have this vague idea of almost being able to get it, I mean it is negative 9 over two, and therefore it would make sense if you times the fraction by the power of two that that would probably include the negative. But I keep writing out this post, thinking I get it, deleting the whole thing and then having second doubts and writing the whole thing out again. I just want to make certain that I understand. I have the lot of trouble in completing the square problems with negatives and positives, I keep getting quite muddled up. *sighs*.