July 13th, 2018, 04:34 AM  #1 
Newbie Joined: Jul 2018 From: Flowbeena Posts: 2 Thanks: 0  Why can't I solve an equation this way?
I don't undertand why I can't solve the equation like I did in the circle. It produces a wrong answer. In my understanding I don't violate a rule by multiplying 2, to get rid of the 2 in the denominator on the left side. 
July 13th, 2018, 06:05 AM  #2 
Math Team Joined: Oct 2011 From: Ottawa Ontario, Canada Posts: 13,608 Thanks: 954 
You've posted "garbage"...please show EXACTLY the original equation. If 2 = (m/2)  (7/7), then: 2 = m/2  1 4 = m  2 m = 6 
July 13th, 2018, 06:06 AM  #3 
Global Moderator Joined: Dec 2006 Posts: 19,974 Thanks: 1850 
You're misunderstanding the notation, Denis. When multiplying or dividing, each term must be used, so you should get 4 = m  14 (which leads to 18 = m, which is correct). 
July 13th, 2018, 06:15 AM  #4 
Senior Member Joined: Apr 2014 From: Glasgow Posts: 2,132 Thanks: 717 Math Focus: Physics, mathematical modelling, numerical and computational solutions 
$\displaystyle 2 = \frac{m}{2}  7$ Multiply both sides by 2: $\displaystyle 2 \times 2 = 2 \times \left(\frac{m}{2}  7\right)$ $\displaystyle 4 = 2 \left(\frac{m}{2}  7\right)$ Expand brackets: $\displaystyle 4 = 2 \times \frac{m}{2}  2 \times 7$ $\displaystyle 4 = \cancel{2} \times \frac{m}{\cancel{2}}  2 \times 7$ $\displaystyle 4 = m  14$ 
July 13th, 2018, 06:16 AM  #5 
Math Team Joined: Oct 2011 From: Ottawa Ontario, Canada Posts: 13,608 Thanks: 954 
Huh? I'm looking at the one on right; I'm assuming it means : 2 = m/2  7/7 Then I'm assuming the OP is trying to solve that.... 
July 13th, 2018, 10:46 AM  #6 
Math Team Joined: Jan 2015 From: Alabama Posts: 3,261 Thanks: 894  Except that then the rest of what is done is nonsense! Also there is a "+" in front of the 7 on the right. I interpret the "/+7" as meaning that he has the equation 2= m/2 7 and that he is adding 7 to both sides. That would give 9= m/2 as on the next line.

July 13th, 2018, 10:55 AM  #7 
Math Team Joined: Oct 2011 From: Ottawa Ontario, Canada Posts: 13,608 Thanks: 954 
Frankly my dear, I don't give a damn 
July 13th, 2018, 12:39 PM  #8 
Math Team Joined: Jan 2015 From: Alabama Posts: 3,261 Thanks: 894 
Your a stern man!

July 13th, 2018, 01:41 PM  #9  
Senior Member Joined: May 2016 From: USA Posts: 1,206 Thanks: 494  Quote:
$2 = \dfrac{m}{2}  \dfrac{7}{.2} \implies 4 = m  \dfrac{14}{.2} \implies$ $m = 4 + \dfrac{14}{.2} = 4 + \dfrac{140}{2} = 74.$ Now if that /. is supposed to mean multiply 2 times both sides of the equation $2 = \dfrac{m}{2}  7 \not \implies 4 = m  7 \implies m = 11.$ Is this standard notation somewhere and the OP simply does not know that $2 \times 7 \ne 7?$  
July 13th, 2018, 01:53 PM  #10 
Math Team Joined: Oct 2011 From: Ottawa Ontario, Canada Posts: 13,608 Thanks: 954  

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