# Homework question

• Aug 31st 2013, 10:39 PM
Hell0
Homework question
Hi everyone, first post here

i'd appreciate it if anyone could help me with this question.

If (x-2A)(2x+1)=2x2-Bx+10, then A • B =

thanks a lot

if this is in the wrong subforum sorry, its precalc homework so i put it here
• Sep 1st 2013, 01:47 AM
chiro
Re: Homework question
Hey Hell0.

Hint: Try expanding both sides and multiply both sides by A so that you can match up the AB term and use the rest of the variables to solve for A,B (remember that in a quadratic, you have fx^2 + gx + c with three constants f,g,c).
• Sep 1st 2013, 08:40 AM
Hell0
Re: Homework question
Hi. this is what i tried

x - 4Ax = -Bx

and

-2A = 10

found a:

A = -5

then plugged it in:

x - 4(-5)x = -Bx
x + 20x = -Bx

pulled out the x because they all have it:

x + 20x = -Bx
1 + 20 = -B
-B = 21
B = -21

-21 * -5 = 105

• Sep 1st 2013, 07:57 PM
ibdutt
Re: Homework question
( x- 2A )( 2x + 1 ) = 2x^2-Bx +10
2x^2 +x - 4Ax - 2A = 2x^2-Bx +10
2x^2 + ( 1 - 4A ) x - 2A = 2x^2-Bx +10
Now compare the coefficients and conclude.
You will get A*B = 105
• Sep 1st 2013, 08:39 PM
Hell0
Re: Homework question
hey thanks everyone. can you try to help me with this one? http://mathhelpforum.com/pre-calculu...-question.html its the only blank question i have left. id really appreciate it
• Sep 2nd 2013, 03:37 PM
Hell0
Re: Homework question
*solved*