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May 15th, 2015, 03:46 AM  #1 
Member Joined: Jan 2015 From: Norway Posts: 95 Thanks: 1  Pull the letters and numbers together
Task 1.28 D) (r +2/ r+3) (r+2/2r+1)= r^2  4/2r^2 + 7r + 3 I understand where all the letters and number come from, expect for 7r. Why is it 7r instead 1r+1= 1r + r = 2r ? Except for that i have done the rest of the task correct, please help me Edit : Here is some tasks i don't understand and solved wrong b) (a/x)+ (4a + 5/ 3x)  (12a/2x)  (7/6x) = 10a/3x C)(6x + 7y +8/2x + y)  (2x + 26y + 16/4x + 2y) + 6 Task 1.30 b) (a/a^2b^2) +(a+b)/ab)^2 = 2a^2 + ab + b^2/(a+b)(ab)^2 The only thing i don't understand with this task is where 2a comes from, the rest i understand. Last edited by Zman15; May 15th, 2015 at 04:28 AM. 
May 15th, 2015, 04:57 AM  #2  
Member Joined: Jan 2015 From: Norway Posts: 95 Thanks: 1  Quote:
I don't understand anything of this task. Should I divide/subtract, what? Help me, please. Last edited by skipjack; May 17th, 2015 at 02:32 AM.  
May 15th, 2015, 06:37 PM  #3 
Senior Member Joined: Nov 2010 From: Indonesia Posts: 2,001 Thanks: 132 Math Focus: Trigonometry  
May 15th, 2015, 06:58 PM  #4  
Math Team Joined: May 2013 From: The Astral plane Posts: 2,138 Thanks: 872 Math Focus: Wibbly wobbly timeywimey stuff.  Quote:
What you wrote: $\displaystyle \left ( x^2  \frac{121}{x^2}  144 \right ) * \left ( 3x + \frac{36}{2x} + 222 \right ) = 3(x  11) (3(x  12))$ What you meant: $\displaystyle \left ( \frac{x^2  121}{x^2  144} \right ) * \left ( \frac{3x + 36}{2x + 222} \right ) = 3(x  11) (3(x  12))$ And the LHS and RHS aren't equal even after it is written correctly. Is there a typo? The RHS of your original question with the r's was even worse. Please use parentheses! Dan Last edited by skipjack; May 17th, 2015 at 02:30 AM.  
May 16th, 2015, 12:03 AM  #5 
Senior Member Joined: Apr 2014 From: Europa Posts: 575 Thanks: 176  With minimal attention to writing, these things can be: $\displaystyle \color{red}{a/x+(4a+5)/(3x)(12a)/(2x)7/(6x)}$ It can be even more clearly: $\displaystyle \color {red}{\dfrac{a}{x}+\dfrac{4a+5}{3x}\dfrac{12a}{2x}\dfrac{7}{6x}}$ This calculation is very simple: 1) The common denominator is 6x. 2) Attention to the minus (in the penultimate fraction). Last edited by skipjack; May 17th, 2015 at 02:54 AM. 
May 16th, 2015, 02:54 AM  #6  
Member Joined: Jan 2015 From: Norway Posts: 95 Thanks: 1  Quote:
Last edited by skipjack; May 17th, 2015 at 02:40 AM.  
May 16th, 2015, 03:46 AM  #7  
Member Joined: Jan 2015 From: Norway Posts: 95 Thanks: 1  Quote:
Thanks, that wasn't hard Last edited by skipjack; May 17th, 2015 at 02:53 AM.  
May 16th, 2015, 05:44 AM  #8  
Math Team Joined: Jan 2015 From: Alabama Posts: 3,264 Thanks: 902  Quote:
Had you actually "got 20/6 as a answer and then divided it with 2" you would have got 20/12= 5/3. You are still being very careless in the way you write numbers and expressions. Quote:
Last edited by skipjack; May 17th, 2015 at 02:42 AM.  
May 16th, 2015, 07:36 AM  #9  
Member Joined: Jan 2015 From: Norway Posts: 95 Thanks: 1  Quote:
Last edited by skipjack; May 17th, 2015 at 02:43 AM.  
May 17th, 2015, 02:51 AM  #10 
Global Moderator Joined: Dec 2006 Posts: 20,469 Thanks: 2038 
$\displaystyle \frac{x^2  121}{x^2  144} \cdot \frac{3x + 36}{2x + 22} = \frac{(x  11)(x + 11)}{(x  12)(x + 12)} \cdot \frac{3(x + 12)}{2(x + 11)} = \frac{3(x  11)}{2(x  12)}$


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