not sure if im just being dumb here tbh lol but can anyone explain this step to me?
1/a + 1/b + 1/c
= (bc + ac + ab) / abc
i just dont see it . shoulda listened at high school
not sure i understand.
so for each fraction you do the same?
so like 1/a = 1/a * bc/bc = bc/abc
then 1/b = 1/b * ac/ac = ac/abc
and 1/c = 1/c * ab/ab = ab/abc
ok it does make more sense but im still confused as to where bc/bc appeared from :/
worse part is i know this is like primary school stuff and i im goin uni doing maths next year :|
Yes, that's the thing.
Now, $\displaystyle \frac{bc}{bc}=1$ and you can multiply any number by 1 without changing its value.
What I've done is to make appear the common factor between a,b and c, that is to say abc, because $\displaystyle \frac mp+\frac np=\frac{m+n}{p}$ and it's only when you have a common denominator that you can add up the fractions.
Try this approach:
$\displaystyle \frac{1}{ab}+\frac{1}{bc}+\frac{1}{ac}$
Find LCD = abc. Multiply that LCD times each term and that becomes your new numerator. The denominator will be your LCD of abc. Let me demonstrate:
$\displaystyle \frac{abc\left(\frac{1}{ab}\right)+abc\left(\frac{ 1}{bc}\right)+abc\left(\frac{1}{ac}\right)}{abc}$
$\displaystyle \frac{c+a+b}{abc}$
$\displaystyle \frac{a+b+c}{abc}$