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x 2 +3x−8=80

 Mar 31, 2015

Best Answer 

 #1
avatar+99377 
+5

$$\\x^ 2 +3x-8=80\\\\
x^ 2 +3x-88=0\\\\$$

 

now I need two numbers that multiply to -88   

(forgetting about the minius sign it could be    8*11,    2*44,   1*88 or  4*22 )

Mmm one must be neg and one must be positive because they mult to a negative.

these numbers must also add to +3.   that means the 'bigger' one is positive.

must be +11 and -8

(x+11)(x-8)=0

x+11=0   or   x-8=0

x=-11       or    x=8

 Mar 31, 2015
 #1
avatar+99377 
+5
Best Answer

$$\\x^ 2 +3x-8=80\\\\
x^ 2 +3x-88=0\\\\$$

 

now I need two numbers that multiply to -88   

(forgetting about the minius sign it could be    8*11,    2*44,   1*88 or  4*22 )

Mmm one must be neg and one must be positive because they mult to a negative.

these numbers must also add to +3.   that means the 'bigger' one is positive.

must be +11 and -8

(x+11)(x-8)=0

x+11=0   or   x-8=0

x=-11       or    x=8

Melody Mar 31, 2015

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