March 12th, 2009, 06:36 PM  #1 
Newbie Joined: Mar 2009 Posts: 24 Thanks: 0  homework help!
how do i times these? i know i use foil but fractions always confuse me! (2x^25x+(x/38/3) 
March 12th, 2009, 07:05 PM  #2 
Senior Member Joined: Feb 2009 From: Adelaide, Australia Posts: 1,519 Thanks: 3  Re: homework help! So... (\frac13x\frac83) \\=(2x^25x+\frac13x  (2x^25x+\frac83 \\=\frac23x^3\frac53x^2+\frac83x \quad  \quad \frac{16}{3}x^2 + \frac{40}{3}x\frac{64}{3} \\\mbox{collecting like terms...} \\=\frac23x^3\frac{21}{3}x^2+\frac{48}{3}x\frac{64}{3} \\=\frac23x^37x^2+16x21\frac13" /> 
March 12th, 2009, 07:40 PM  #3 
Newbie Joined: Mar 2009 Posts: 24 Thanks: 0  Re: homework help!
ok but home 2x^2 became 2/3x^3?

March 12th, 2009, 07:48 PM  #4 
Senior Member Joined: Feb 2009 From: Adelaide, Australia Posts: 1,519 Thanks: 3  Re: homework help! \frac13x \\=\frac23x^3\frac53x^2+\frac83x" /> The first term in the brackets: Multiplied by 
March 13th, 2009, 04:12 AM  #5  
Senior Member Joined: Mar 2009 Posts: 318 Thanks: 0  Quote:
Quote:
Code: 2x^2  5x + 8 (1/3)x  8/3  Code: 2x^2  5x + 8 (1/3)x  8/3   (16/3)x^2 + (40/3)x  64/3 Code: 2x^2  5x + 8 (1/3)x  8/3   (16/3)x^2 + (40/3)x  64/3 (3/2)x^3  (5/3)x^2 + (8/3)x   
March 13th, 2009, 06:55 AM  #6 
Global Moderator Joined: Dec 2006 Posts: 20,370 Thanks: 2007 
(2x²  5x + 8)(x/3  8/3) = (2x²  5x + 8)(x  8)/3 (this defers working with fractions). Each term within the second set of parentheses has to be applied to each term within the first set (or vice versa). We systematically choose the pairs of terms that will combine to produce as high a power of x as possible (without choosing the same pair again, of course), and combine like powers. The results are written within parentheses and then the division by 3 is appended. Thus, one writes (2x² * x + 2x² * (8)  (5x)x + 8*x  (5x) * (8) + 48x + 8 * (8))/3, which simplifies to (2x³  21x² + 48x  64)/3, which equals (2/3)x³  7x² + 16x  64/3. The final term can be written as 21 1/3 if you like. With practice, much of the above can be done mentally, allowing the entire calculation to be written on one line. 
March 13th, 2009, 10:55 AM  #7  
Senior Member Joined: Sep 2008 Posts: 116 Thanks: 0  Re: homework help! Quote:
 

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