Question

how to factor -x^2 - 2x + 15

Answer 1

First divide everything by -1.

Answer 2

You get x^2+2x-15

Answer 3

It factors then as (x+5)(x-3) and you're done.

Answer 4

(-x-5)(x-3)

Answer 5

(-x-5)(x-3)

Answer 6

No, you need to factor a (-1) out of your (-x-5) term. Your leading term cannot be negative.

Answer 7

Well, then you'd better include it in your final answer (-1)(x+5)(x-3).

Answer 8

No, because you can't factor originally with a negative x^2.

Answer 9

So that factoring is wrong.

Answer 10

-(x+5)(x-3)

Answer 11

-(x+5)(x-3) this is the right answer i think but how

Answer 12

Well you can begin like OakTree and pull out the -1: -(x^2+2x-15);
then you are looking for something like (x+a)(x+b) but what are a and b?
Consider what that looks like when multiplied out: x^2+ax+bx+ab.
The x^2 is right.
ax+bx has to equal 2x; therefor a+b=2
ab must equal -15
So consider the factor pairs of -15 that could be a and b: 1,-15; -1,15; 3,-5; -3,5
Only the last pair adds to 2, so it must be -(x-3)(x+5)

Answer 13

thanks

Answer 14

-x^2 - 2x + 15 = -(x^2+2x-15) = - (x-5)(x+3)

Answer 15

no, both x's would be negative

Answer 16

no negative outside

Answer 17

it's ok to have negative outside too, both ways work.