Math Is Fun Forum

bananaphone

Member

Registered: 2008-04-30

Posts: 1

quick help with roots

bananaphone

messege deleted

Last edited by bananaphone (2008-05-01 08:05:20)

simron

Real Member

Registered: 2006-10-07

Posts: 237

Re: quick help with roots

Here's a few tips:
First, set each f(x)=0. This is where the graph crosses the x-axis.
Now either factor, complete the square, or use the quadratic formula:

Last edited by simron (2008-04-30 08:41:53)

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Linux FTW

bananaphone

Member

Registered: 2008-04-30

Posts: 1

Re: quick help with roots

I got -1,-10 is that right?

Ricky

Moderator

Registered: 2005-12-04

Posts: 3,791

Re: quick help with roots

simron, these were meant to be factored without the quadratic method.

bananaphone, you need to make the equations into the following form:

(x - a)(x - b)

So if we were to multiply this out, we get:

x^2 - (a+b)x + ab

So if you look at the first one, we see that ab = -11, and so one possibility for a and b is 1 and -11.  Now we need a + b to be -10.  But 1 + -11 = -10, as we needed.  SO

x^2 - (1 + -11)x + 1*-11 = x^2 + 10x - 11

And we get:

x^2 + 10x - 11 = (x - 1)(x+11)

This tells us the roots are 1 and -11.

There is no square key on my laptop

Your keys are round?

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"In the real world, this would be a problem.  But in mathematics, we can just define a place where this problem doesn't exist.  So we'll go ahead and do that now..."

bananaphone

Member

Registered: 2008-04-30

Posts: 1

Re: quick help with roots

no my keys are square wtf?

Ricky

Moderator

Registered: 2005-12-04

Posts: 3,791

Re: quick help with roots

...just a joke...

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"In the real world, this would be a problem.  But in mathematics, we can just define a place where this problem doesn't exist.  So we'll go ahead and do that now..."