Hey all.

I have a problem with maths.
I have 2 problems actually lol.
If I have this thing (x+20) (x-3) how would I know wheter it's
x^2+3x-20x-60 or if it's x^2-3x+20x+60?
The second problem is we have this method called sum product method freely translated.
If I have something like X^2-21x+20.
I need to look it up in some tabel what the answer is.
But I don't know how that tabel works.
It goes like this:
1 15 16
-1 -15 -16
3 5 8
-3 -5 -8

Anyway, the first one is x^2+17x-60, thats all it can be. (The two integers have different signs, so you know the answer must be negative.)

Not sure I understand your second question...
It's x^2 + 17x - 60.
Not sure about the next bit, never seen it before.
But it's a quadratic with the factors being: (x-20)(x-1)
Last edited by conor-figgy at Jun 7, 2011,
(x+20)(x-3)
= (x*x) + (x*-3) + (20*x) + (20*-3)
= x^2 - 3x + 20x - 60
= x^2 + 17x - 60

The second one made no sense, did you translate it from another langauge?
Last edited by GisleAune at Jun 7, 2011,
Quote by liampje
If I have this thing (x+20) (x-3) how would I know wheter it's
x^2+3x-20x-60 or if it's x^2-3x+20x+60?

The signs go with the numbers after them.
So +x multiplies with +x and you get x^2
Then the first +x multiplies with -3, and you get -3x
The second +x multiplies with +20 and you get +20x
You can combine the two x's (20x and -3x) to get a positive 17x.
Then you just multiply the +20 and -3 to get -60.

So the whole equation would be:
x^2 + 17x - 60

This is 7th-8th grade stuff.

I don't understand your other question, as i've never heard of this table.

EDIT: FFFUUUUUU-
I knew I was wasting my time typing it all out with words.
The 2nd question x^2-21x+20 must be equal to something?
Check if there's anything on the RHS.
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Example:

x^2+11x+10

x^2 means there must be (x )(x )
11x+10 means that the numbers must add together to be 11, and multiplied together to make 10. In this case, that gives us 10 and 1.

So: (x+10)(x+1)

If you have something like 2x^2, then it gets a little bit more involving, as that 2x will affect other parts:

2x^2+12x+10

(2x )(x )

Now, as there is a 2x, you need to do a bit of thinking. The numbers must multiply to become 10, but must add to become 12 when one is doubled due to that 2x.

5x2=10
10x1=10

Now I've written all this out I've inadvertantly done an example with two answers

(2x+2)(x+5)
(2x+10)(x+1)
Last edited by Deliriumbassist at Jun 7, 2011,
the second one looks like you may have to substitute those values in for x to solve? thats my guess
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