fraction exponent question

• December 9th 2010, 03:58 PM
fran1942
fraction exponent question
Hello, I cannot understand the circled stage of this equation.

Thanks kindly for any help.
• December 9th 2010, 04:04 PM
Prove It
They need to get everything to the smallest possible base. Notice that $\displaystyle 4 = 2^2$.

So $\displaystyle \frac{4^3 \times 5^2 \times 2^3}{3^3 \times 3^2 \times 5^3} = \frac{(2^2)^3 \times 5^2 \times 2^3}{3^3 \times 3^2 \times 5^3}$.

The next step is to cancel as many of the $\displaystyle 5$s as possible. Since there are $\displaystyle 3$ on the bottom and $\displaystyle 2$ on the top, that means you can cancel $\displaystyle 2$ of them and be left with $\displaystyle 3-2 = 1$ of them on the bottom.

Does it make a bit more sense now?
• December 9th 2010, 04:12 PM
e^(i*pi)
Numerator

As $4 = 2^2$ you can write $4^3 = (2^2)^3$

Hence the numerator becomes $(2^2)^3 \times 2^3 = 2^9$

Denominator:

As $a^{b+c} = a^ba^c$ it can be rewritten as $3^3 \times 3^2 = 3^{3+2}$

$5^{3-2}$ comes from $5^2$ in the numerator so in the denominator it may be written as $5^{-2}$ and put in the denominator. Combined with $5^3$ we can put $5^{3-2}$ on the denominator

In total we get

$\dfrac{(2^2)^3 \times 2^3}{3^{3+2} \times 5^{3-2}}$ which is the question.

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Personally though I'd have cancelled out 5^2 from top and bottom thus eliminating the need to deal with powers of 5.
• December 9th 2010, 04:32 PM
fran1942
thanks very much for your help, however I dont understand why the (5 to power of 3-2) would not be (5 to power of 2-3).

Regards
• December 9th 2010, 04:42 PM
e^(i*pi)
Just look at the terms with 5 in you have $\dfrac{5^2}{5^3}$. You can write that at $5^{2-3}$ if you like - as long as you leave it in the numerator.

If you want to look at the denominator (which is what the question does) then you will have to take the reciprocal of $5^{2-3}$ which is $5^{3-2}$ and put this term on the denominator.

If you can use your own working you'll save yourself a lot of time by saying that $\dfrac{5^2}{5^3} = \dfrac{1}{5}$
• December 9th 2010, 04:42 PM
pickslides
$5^{2-3} = \frac{1}{5^{3-2}}$