Need help with solving quadratic equations on Khan Academy

Question

In the screenshot below, you'll see the correct answer is x = -9 or x = -7. I wrote x = -7 or x = -9 and got it wrong.

I do not understand why one is right and the other is wrong as it doesn't matter which order you write them in the factored expression: (x + 9)(x + 7) = (x + 7)(x + 9), right?

enter image description here

It's a software issue. Mathematically it does not matter if you first write $-7$ and then $-9$ or the other way around... — imranfat, Oct 27 '16 at 01:01
The order doesn't matter, unless the problem states that it does. From the image you linked: give the solutions in ascending order. — dxiv, Oct 27 '16 at 01:02
The order doesn't matter. I guess some people prefer to write the lower number to the left. — AfronPie, Oct 27 '16 at 01:02
"Give solutions in ascending order", it says, although that shouldn't matter much. The answers are correct, though in the wrong order. — Sarvesh Ravichandran Iyer, Oct 27 '16 at 01:03
Mathematically, it's correct. For the purposes of making their checking software more straightforward, they probably put the ascending requirement. — Nitin, Oct 27 '16 at 01:05

score 1 · Answer 1 · answered Oct 27 '16 at 02:11

Both of your roots are correct. However, the automatized grading system asked for them in "ascending order." Therefore, for the system to recognize your answers as correct, you would need to put $-9$ in the first box and $-7$ in the second box since $-9<-7$.

Need help with solving quadratic equations on Khan Academy

1 Answers1