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What is the missing coefficient in the above expression? (3x2-4x+7)(-2x2+5x-9) = -6x4+23x3+______x2+71x-63

 Jan 6, 2015

Best Answer 

 #2
avatar+28125 
+5

$$(3x^2-4x+7)(-2x^2+5x-9)=-6x^4+23x^3-61x^2+71x-63$$

 

Think of this as:

$$3x^2(-2x^2+5x-9)-4x(-2x^2+5x-9)+7(-2x^2+5x-9)$$

 

Then multiply the 3x2 by all the terms inside the brackets; do the same for the -4x and the +7; then collect like terms together.

.

 Jan 7, 2015
 #1
avatar+360 
0

 I dont think that is possible all the numbers I put in = to at least somewhere around 4000 while the answer has to at least be 1,078

 #2
avatar+28125 
+5
Best Answer

$$(3x^2-4x+7)(-2x^2+5x-9)=-6x^4+23x^3-61x^2+71x-63$$

 

Think of this as:

$$3x^2(-2x^2+5x-9)-4x(-2x^2+5x-9)+7(-2x^2+5x-9)$$

 

Then multiply the 3x2 by all the terms inside the brackets; do the same for the -4x and the +7; then collect like terms together.

.

Alan Jan 7, 2015

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