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#1 2013-07-13 12:23:51

bronxsystem
Member
Registered: 2013-06-22
Posts: 63

Multiplying fractions

Hey all i know this is really basic but i have hit a wall

(d / a+b) * (5a + 5b / 2d^2 + 2d)

i can get the answer but im not sure what im actually doing S:

i khow to multiply problem like (1/2) * (1/2) = 1/4 but what confuses me in this problem is the denominator a+b not sure how to multiply the other denominator with it.

My workings

(d / a+b) * (5a + 5b / 2d^2 + 2d)

i just divide by common factors first step
numerator 5a + 5b to 5 ( a+b)
then denominator 2d (d + 1)

then i just divided both numerator and denominator by common factors (a+b) and d
so i got the answer 5 / 2 (d + 1)

how would you guys solve it? sorry if my reasoning bit over the place, any chance you can show me your working so i can aware myself.

thank you.

Last edited by bronxsystem (2013-07-13 12:25:09)

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#2 2013-07-13 12:35:24

bronxsystem
Member
Registered: 2013-06-22
Posts: 63

Re: Multiplying fractions

had another one that the method works but again not sure what im doing S:
( a + 3 / a - 5) * (2a - 10 / 3a + 9)

= (a + 3 / a - 5) * 2 ( a - 5) / 3 (a + 3)

then just divide numerator and denominators by common factors and i get 2/3

>< whats this called or what rule is it?

Last edited by bronxsystem (2013-07-13 12:42:23)

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#3 2013-07-13 16:00:00

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 86,228

Re: Multiplying fractions

Hi;

I would call it cancellation.


In mathematics, you don't understand things. You just get used to them.
Of course that result can be rigorously obtained, but who cares?
Combinatorics is Algebra and Algebra is Combinatorics.

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#4 2013-07-14 00:30:38

bronxsystem
Member
Registered: 2013-06-22
Posts: 63

Re: Multiplying fractions

sorry those other 2 post had to much fluff a better question maybe is do you think the steps i take are acceptable?

eg

(3ab^2 / 4) * ( 12/ 18a^2)

just simply multiply numerators then denominators and then simplify

(36ab^2) / (72a^2)

then divide by common factor 36a

= b^2 / 2a

thats all it is right?






not sure why this way works i thought your meant to divide both numerator and denominator by same number S:

(3ab^2 / 4) * (12 / 18a^2)

first divide numerators by common factor 3

4ab^2

then divide denominators by common factor 2
2 (8a^2)

then divide both numerators and denominators by 2
(2ab^2 / 4a^2)

then divide by 2a
( b^2 / 2a)

Last edited by bronxsystem (2013-07-14 00:47:35)

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#5 2013-07-14 04:19:09

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 86,228

Re: Multiplying fractions

The first method is simpler.


In mathematics, you don't understand things. You just get used to them.
Of course that result can be rigorously obtained, but who cares?
Combinatorics is Algebra and Algebra is Combinatorics.

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#6 2013-07-14 04:22:53

bronxsystem
Member
Registered: 2013-06-22
Posts: 63

Re: Multiplying fractions

roger thanks

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#7 2013-07-14 04:27:24

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 86,228

Re: Multiplying fractions

You are welcome.


In mathematics, you don't understand things. You just get used to them.
Of course that result can be rigorously obtained, but who cares?
Combinatorics is Algebra and Algebra is Combinatorics.

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