leaving 4th and 2nd terms: 1/(3b) - 3/(4b)

Is that clearer?

Solved

Posted on 2011-04-28

How does this = a/b-5/12b third line down? I figured out the -5/12b part, because 12b is the common factor when subtracting -3/4b+1/3b. It looks like they are trying to add a/2b + a/2b.

a/2b + a/2b = 2a/2b not a/b. This can't be reduced can it because the numerator and denominator have different letters?

How do they get a/b? Thanks.

01.jpg

a/2b + a/2b = 2a/2b not a/b. This can't be reduced can it because the numerator and denominator have different letters?

How do they get a/b? Thanks.

01.jpg

17 Comments

leaving 4th and 2nd terms: 1/(3b) - 3/(4b)

Is that clearer?

1/(2b) = (1/2)*(1/b)

and

(2a)/b = 2*(a/b)

putting it together:

(2a)/(2b) = 2*[ a/(2b) ] = 2*a*[ 1/(2b) ] = 2*a*[ (1/2)*(1/b) ] = 2*a*(1/2)* [ (1/b) ] =

= a* [ (1/b) ] = a/b

=2a/4b

Your above 2 lines show the Right Hand Side of the = sign. It is important that you have a both a RHS and a LSH when writing an = sign.

What are the LHS's of the = sign?

= 2 [ a/(2b) ] = a/b here 2*a and 2*2b = 2a/4b. or so I thought.

=2a/4b

true.

===

= 2 [ a/(2b) ] = a/b here 2*a and 2*2b = 2a/4b. or so I thought.

=2a/4b

2 [ a/(2b) ] =

2 a

------ * --------

1 2b

One 2 is in the numerator; the other is in the denominator, so they cancel out.

http://www.wtamu.edu/acade

It helps to plug in numbers as a check:

Let a = 36 and b = 4

Is (2a)/(2b) = (a/ b) ?

(2a)/(2b) = (2*36)/(2*4) = 72/8 = 9

a/b = 36/4 = 9

So, at least for that a and b, it checks out OK.

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