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the polynomial x^3+ax^2-bx=6 has factors of (x+1) (x+2) what is a and b

 Oct 23, 2016
 #1
avatar+23254 
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The polynomial  x3 + ax2 - bx  =  6

      --->                x3 + ax2 - bx - 6  =  0

Since it has the factors  (x + 1)(x + 2),  we need to find the third factor.

     (x + 1)(x + 2)     --->     x2 + 3x + 2

The third factor must have just  x  for the x-term (to get a final product of   x3)

and a number factor of  -3  (to get a final product of  -6).

The third factor is:  x - 3.

Multiplying the factors  (x + 1)(x + 2)(x - 3),  we get:  x3 + 0x2 - 7x - 6.

Therefore, the value of  a  is  0     and     the value of  b  is  -7.

 Oct 23, 2016
 #2
avatar+26396 
0

the polynomial x^3+ax^2-bx=6 has factors of (x+1) (x+2) what is a and b

 

I. factors of (x+1)x1=1

x3+ax2bx6=0|x1=1(1)3+a(1)2b(1)6=01+a+b6=0a+b7=0|+7a+b=7b=7a

 

 II. factors of (x+2) (x+2)x2=2

x3+ax2bx6=0|x2=2(2)3+a(2)2b(2)6=08+4a+2b6=04a+2b14=0|+144a+2b=14|:22a+b=7|b=7a2a+7a=7a+7=7|x2=7a=0a=0b=7a|a=0b=70b=7b=7

 

x3+ax2bx=6|a=0b=7x3+0x27x=6x37x=6

 

laugh

 Oct 24, 2016

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