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Show that this quadratic factors to P = -5(x-9)(x-3).A company named Music Madness is a...

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paulbarton | (Level 1) Honors

Posted October 21, 2012 at 3:14 PM via web

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Show that this quadratic factors to P = -5(x-9)(x-3).

A company named Music Madness is a company that makes CD players. Last year, accountants modeled the company's profit by P= -5x^2+60x-135.

Please explain fully how to answer this question. Thank you.

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jeew-m | College Teacher | (Level 1) Educator Emeritus

Posted October 21, 2012 at 3:35 PM (Answer #1)

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`P = -5x^2+60x-135`

Get (-5) out as a factor from the left side.

`P = (-5)((-5x^2)/(-5)+(60x)/(-5)-135/(-5))`

P = -5(x^2-12x+27) ----(1)


Now you should find two numbers which gives its addition as -12 and product as 27.

Addition -12 means the number before x in (1)

Product 27 means the number without x terms in (1)

`27 = 9xx3` which gives addition 9+3 = 12

`27 = (-9)xx(-3)` which gives addition (-9)+(-3) = -12


So the to numbers are (-9) and (-3).


Now e should rearrange (1) as the following.

P = -5(x^2-12x+27)

P = -5(x^2-9x-3x+27)


Now consider only the bracket.


= x(x-9)-3(x-9) 

you can see above in the first line x is common for the bold part and -3 is common for the italic part.

Then you will see (x-9) is common again for the second line.



= x(x-9)-3(x-9) 

= (x-9)(x-3)


So bracket can be rewritten as ;

`x^2-9x-3x+27 = (x-9)(x-3)`


P = -5(x^2-9x-3x+27)

P = -5(x-9)(x-3)

So this is the answer what we want.






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