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Find the factors ? x^2-2x-3 ??

TandCforlife  Mar 27, 2017
 #1
avatar+26750 
+1

x2 - 2x - 3 → (x - 3)(x + 1)

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Alan  Mar 27, 2017
 #2
avatar+50 
+1

Thx so much do u know these by any chance ? 

 

x^2+2x-8    x^2+x-8     x^2-4 ???    Pls ?

TandCforlife  Mar 27, 2017
edited by TandCforlife  Mar 27, 2017
 #3
avatar+26750 
+1

Think of these as (x - a)(x - b) → x2 - (a+b)x +a*b

 

(1) Compare with  x2 + 2x - 8  

 

We must have a*b = -8  so what are the possible products:

-8  and 1 

8 and -1 

-4 and 2

4 and -2

 

We must also have -(a + b) = 2 so, using the above possible products:

-8 and 1  give -(-8 + 1) → 7  no!

8 and 1 give -(8 + 1) → -9 no!

-4 and 2 give -(-4 + 2) → 2  yes!

4 and -2 give -(4 - 2) → -2 no!

 

So we have x2 + 2x - 8 → (x - -4)(x - 2) → (x + 4)(x - 2)

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Try this yourself with x2 - 4

 

x2 + x - 8 doesn't have nice integer roots.  You can do this using the quadratic formula, for example.

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Alan  Mar 27, 2017

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