I don't understand this reasoning.

Alfonso

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Jul 29, 2015
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Hi fellow math lovers,

So I was making my some math problems, and suddenly.. BOOM, a problem which seems intractable.
Now it might be that I do not understand some rule or the full extent of a certain rule. In any event.. I hope you can help me understand the reasoning behind parts of the following 2 problems; see below.
(The problems are fully solved for, so just to be sure, I'm not trying to get copy and paste answers. I just don't know why these operations work.) Oh! and I hope you can read my handwriting:p

The first problem:
attachment.php

What I don't understand here is, first of all, why the second (minus square root) B is not included in the next (second) step? What happens to it and why?
From there, as you see, I have tried to decipher it as far as I can, noticing that the -1 in the second step comes from the (minus square root) B. The other stuff I completely understand, just that damned (minus square root) B!


The second problem:

attachment.php

What I don't understand with this one is why you are allowed to turn both fractions upside down, doesn't this change the value?
I'm solving for y here (obviously). You can see that I fully understand that after that particular step the 4 under y goes away through multiplication. So yeah.. maybe someone can show me why you can turn a fraction upside down with a simpler example?

Thanks a lot! If the pictures need to be bigger, command, and it will be so.

Greetings,
Alfonso Copernicosis.
 

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They factored. Just as 4Ax - x would be x(4A - 1), so also 4Asqrt - sqrt = sqrt(4A - 1). ;)
 
Regarding the second part of your question

Hi fellow math lovers,


The second problem:

attachment.php

What I don't understand with this one is why you are allowed to turn both fractions upside down, doesn't this change the value?
I'm solving for y here (obviously). You can see that I fully understand that after that particular step the 4 under y goes away through multiplication. So yeah.. maybe someone can show me why you can turn a fraction upside down with a simpler example?

Thanks a lot! If the pictures need to be bigger, command, and it will be so.

Greetings,
Alfonso Copernicosis.

Greeting and salutations Alfonso Copernicosis,

The "flip" is a short cut, you could achieve the same result by multiplying both side of

eq1: 4/y = (1-5x)/5,

first by (y/4) and then by (5/(1-5x)).
 
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