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July 13th, 2018, 03:34 AM   #1
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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.
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July 13th, 2018, 05:05 AM   #2
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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
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July 13th, 2018, 05:06 AM   #3
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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).
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July 13th, 2018, 05:15 AM   #4
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$\displaystyle 2 = \frac{m}{2} - 7$

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:
$\displaystyle 4 = 2 \times \frac{m}{2} - 2 \times 7$

$\displaystyle 4 = \cancel{2} \times \frac{m}{\cancel{2}} - 2 \times 7$

$\displaystyle 4 = m - 14$
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July 13th, 2018, 05:16 AM   #5
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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....
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July 13th, 2018, 09:46 AM   #6
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Quote:
Originally Posted by Denis View Post
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....
Except that then the rest of what is done is non-sense! 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.
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July 13th, 2018, 09:55 AM   #7
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Frankly my dear, I don't give a damn
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July 13th, 2018, 11:39 AM   #8
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Your a stern man!
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July 13th, 2018, 12:41 PM   #9
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Quote:
Originally Posted by skipjack View Post
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).
I must admit that I cannot make heads or tails out of the notation either.

$2 = \dfrac{m}{2} - \dfrac{7}{.2} \implies 4 = m - \dfrac{14}{.2} \implies$

$m = 4 + \dfrac{14}{.2} = 4 + \dfrac{140}{2} = 74.$

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
$2 \times 7 \ne 7?$
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July 13th, 2018, 12:53 PM   #10
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Your a stern man!
I'm more a utern guy
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