#1
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
Please help.
#2
MATHS THREAD.

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...
#3
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,
#5
(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,
#6
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.
#7
The 2nd question x^2-21x+20 must be equal to something?
Check if there's anything on the RHS.
Gear:
Ibanez RGT6EX
Line 6 Spider 3 15
Hobner 265

Quote by Lost Dog
People absolutely love to see horrible accidents and murders, as well as any sort of fighting really. Just look at the news. We wouldn't watch it if it was boring.
#8
Quadratics is easy:

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,
#9
the second one looks like you may have to substitute those values in for x to solve? thats my guess
My Gear:

Fretless Squier P Bass
Ibanez SR400QM
Gallien Krueger 1001RB
Traynor TC410
Digitech Whammy
Boss DD-7