Factorise x2 + 2x - 15?

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

x^2 + 2x - 15 =

(x + 5)(x-3)

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

It's hard to explain these - although it would help if you put a "^" in front of yoru exponent. You need to find two numbers whose product is -15 and whose sum is +2

5 and -3 come to mind - that's really the tricky part. You just need to practice these until you can find factors of a number so the middle term works out.

Anyway, this makes the answer (x+5)(x-3)

It gets tricky when you have to consider all possible combinations of factors, but eventually it will fall into place. Keep practicing.

( x + 5 ) ( x - 3 )

The best way to factor this is by trial and error since there are a limited number of options available. To start, we know that 15=15*1 or 15=3*5. Therefore, we know we should have 1 and 15, or 3 and 5 appearing in our factorization. We know x^2=x*x, so as the first step, we could write:

x^2+2x-15=(x )(x ).

Observe 2x as the middle term. No matter how we manipulate 1 and 15, we cannot obtain the coefficient of positive 2 we are looking for. But, 2=5-3=5+(-3). Hence,

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

Using FOIL, we can verify that the answer is correct.

:-)

You have to take this in steps. First, start with the x2. You know right away that you'll have to have x times x to get this, so the factors will be (x + ?)(x + ?).

The tricky part is figuring out the 2x and -15. You'll have to figure out two numbers than when multiplied = -15, but when multipled by x = 2 when added. This is sort of confusing, but hopefully I can explain it better.

What two numbers = -15? Lets start with -1 and 15. If you put those into the equation we figured out previously of (x + ?)(x +?) you get (x + -1)(x + 15). But this would be x2 + -1x +15x - 15 which is x2 + 14x -15 if you simplified it. (Hopefully you understand this part) This isn't what we're looking for of course. Continue to come up with numbers that = -15 when multipled until you get a x2 + 2x - 15.

The answer is (x + -3)(x + 5). This would give x2 - 3x + 5x -15 or simplified, x2 + 2x - 15.

x2 + 2x - 15 = (x + 5)(x-3)

Why????
because....

x * x = x2
x * -3 = -3x
5 * x = 5x
5 * -3 = -15

That's....

x2 + 5x - 3x - 15

then...

x2 + 2x - 15

Good luck!

here,
x^2+2x-15
x^2+(5-3)x-15
x^2+5x-3x+15
x(x+5)-3(x+5)
take common factor,
(x+5)(x-3)
therefore,x^2+2x-15=(x+5)(x-3)

note that factors of -15 are 1,-15 ; 3,-5 ; -1,15 ; -3,5
we take 5 and subtract 3 to get 2
x2 + (5-3)x - (5*3)

so we have (x+5)(x-3)
these will multiply out to give you x² + 2x - 15

I hope you saw the method to doing that one, as quadratic equations aren't that difficult and quite necessary for your entire school career...

Good Luck
-J