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Mathematics 18 Online
OpenStudy (joftheworld):

@phi [attachment]

OpenStudy (joftheworld):

OpenStudy (phi):

how far can you get ?

OpenStudy (joftheworld):

\[9a ^{4}b ^{5} \] ??

OpenStudy (joftheworld):

is that right ?

OpenStudy (phi):

can you show your steps?

OpenStudy (joftheworld):

\[\sqrt{3^{4}*a ^{8}b ^{10}} \] \[^{2/2}\sqrt{3a ^{4/2}*a ^{8/2}b ^{10/2}}\]

OpenStudy (phi):

ok, pretty close. But they want the 4th root \[ \sqrt[4]{stuff} \]

OpenStudy (joftheworld):

oh..

OpenStudy (phi):

and when you "divide the exponents" by the root, you *drop the radical* sign. remember \[ \sqrt[4]{3^4 a^8 b^{10}}= \left(3^4 a^8 b^{10}\right)^\frac{1}{4} \]

OpenStudy (phi):

when I do these, I switch to the "exponent" form. simplify. then switch back to radical form

OpenStudy (joftheworld):

\[3^{1/4} * a ^{3}b ^{5/2}\]

OpenStudy (phi):

go slower. Do you understand this step: \[ \sqrt[4]{3^4 a^8 b^{10}}= \left(3^4 a^8 b^{10}\right)^\frac{1}{4} \\ = \left(3^4\right)^\frac{1}{4}\left(a^8\right)^\frac{1}{4}\left(b^{10}\right)^\frac{1}{4} \]

OpenStudy (phi):

and now use the rule \[ \left(a^b\right)^c = a^{bc} \]

OpenStudy (joftheworld):

is is that the final answer ?

OpenStudy (phi):

not yet. But we have to leave some work for you, right?

OpenStudy (joftheworld):

im doing the best i can D:

OpenStudy (phi):

so far we have \[ \left(3^4\right)^\frac{1}{4}\left(a^8\right)^\frac{1}{4}\left(b^{10}\right)^\frac{1}{4} \] now use the rule \[ \left(a^b\right)^c = a^{bc} \] to simplify just this part \[ \left(3^4\right)^\frac{1}{4} \]

OpenStudy (joftheworld):

3 ?

OpenStudy (phi):

match 3 with a, 4 with b, and c with ¼ the rule says we get 3^(4*¼) = 3^1 = 3

OpenStudy (phi):

now do the (a^8)^(¼) same rule

OpenStudy (joftheworld):

\[a ^{2}\] ?

OpenStudy (phi):

yes

OpenStudy (phi):

now the last part (b^10)^(¼)

OpenStudy (joftheworld):

\[b ^{5/2}\] ?

OpenStudy (phi):

yes, but write 5/2 as a "mixed number" rather than as an improper fraction

OpenStudy (phi):

or, better, as a the sum of a whole number and a fraction

OpenStudy (joftheworld):

im confused.. i got like 3 answers..

OpenStudy (phi):

so far we have \[ \left(3^4\right)^\frac{1}{4}\left(a^8\right)^\frac{1}{4}\left(b^{10}\right)^\frac{1}{4} = 3 a^2 b^\frac{5}{2} \] but we should write 5/2 as 2 + ½ (which is the same thing as 5/2 , right?)

OpenStudy (phi):

\[ \left(3^4\right)^\frac{1}{4}\left(a^8\right)^\frac{1}{4}\left(b^{10}\right)^\frac{1}{4} = 3 a^2 b^2 b^\frac{1}{2} \]

OpenStudy (phi):

is something puzzling you ?

OpenStudy (joftheworld):

which still equals to \[3a^2b ^{5/2}\]

OpenStudy (phi):

yes, but they probably want to simplify as much as possible in other words be write \[ b^\frac{5}{2} = b^{2 + \frac{1}{2}}= b^2 b^\frac{1}{2} \]

OpenStudy (phi):

and the final answer (using radicals) is \[ 3 a^2 b^2 \sqrt{b} \]

OpenStudy (joftheworld):

thanks. what about this one ?

OpenStudy (phi):

let's do it step by step. first change 256 to 2^ some number then rewrite the radical as ( stuff) ^ (¼)

OpenStudy (joftheworld):

to 2 ?

OpenStudy (joftheworld):

hows that ?

OpenStudy (joftheworld):

divide ?

OpenStudy (phi):

we should factor 256 into its prime factors. (which is only 2) in other words, 256= 2* 128= 2*2*64... keep going

OpenStudy (joftheworld):

16 ?

OpenStudy (joftheworld):

2x2x39 ?

OpenStudy (phi):

are you asking how to divide 2 into 64? we (so far) have 256= 2* 128 (check with a calculator) but 128 is 2* 64, so 256= 2* 2*64 now factor 64 into 2 and another number

OpenStudy (joftheworld):

so then 2x2x2x32 then 2x2x2x2x16 ?

OpenStudy (phi):

yes, but 16 can be simplified to 2*8

OpenStudy (joftheworld):

so then itll be 2x2x2x2x2x8

OpenStudy (phi):

and (cutting to the chase!) 8 = 2x2x2

OpenStudy (joftheworld):

okayy

OpenStudy (phi):

and 256= 2x2x2x2x2x2x2x2 and now we see why people invented exponents. It 's easier to type 256= \(2^8\)

OpenStudy (joftheworld):

so then itll be \[2^{8}a ^{6}b ^{12}c ^{2}\]

OpenStudy (phi):

yes, but with either a radical sign around it (and a little 4 to show 4th root) or put parens around it , and write to the ¼ power

OpenStudy (phi):

\[ \left( 2^8 a^6 b^{12} c^2\right)^\frac{1}{4} \] then multiply the ¼ times each exponent inside

OpenStudy (joftheworld):

\[4a ^{1/4}b ^{1/4}c ^{1/2}\]

OpenStudy (joftheworld):

sorry 4a^3/2

OpenStudy (phi):

ok on the 4, the a and the c. re-do the b

OpenStudy (joftheworld):

b^3 ?

OpenStudy (phi):

yes. what do we have so far (all together)?

OpenStudy (joftheworld):

\[4a ^{3/2}b ^{3}c ^{1/2}\]

OpenStudy (phi):

looking good. now write a^(3/2) using whole number plus a fraction

OpenStudy (phi):

in other words divide 2 into 3 to get 1 with a remainder of 1 we write 3/2 = 1 + ½

OpenStudy (joftheworld):

1.5 ?

OpenStudy (phi):

yes, but we want to use fractions (not decimals) because we will be changing back to "radical form" and we need a fraction to do that. anyways, a^(3/2) = a^(1+ ½) = a^1 a^(½) or a x a^(½)

OpenStudy (phi):

now (all together ) what do we have ?

OpenStudy (joftheworld):

1(1/2) ?

OpenStudy (phi):

are you still working on the 3/2 = 1 + ½ ? as posted above, we used that to rewrite \[ a^\frac{3}{2} = a^{1 + \frac{1}{2}} = a^1a^\frac{1}{2}= a a^\frac{1}{2} \]

OpenStudy (phi):

now that we have rewritten the a part, what do we have for the whole answer?

OpenStudy (joftheworld):

a^(3/2) ?

OpenStudy (phi):

we want to finish the problem \[ 4a ^{3/2}b ^{3}c ^{½} \\ 4a\ a^{1/2}b ^{3}c ^{1/2}\] or after changing the order \[ 4ab ^{3}\ a^{1/2}c ^{1/2}\] any idea what next ?

OpenStudy (joftheworld):

\[4aa ^{1/2}b^3c ^{1/2}\]

OpenStudy (phi):

We could be done here, but they probably want you to replace the fraction exponents with radicals.

OpenStudy (joftheworld):

yeah ..

OpenStudy (phi):

which is why I wrote the answer in this order \[ 4ab ^{3}\ a^{½} c ^{½} \] the a^½ turns into a square root. same for the c^1/2

OpenStudy (joftheworld):

which im still confused..

OpenStudy (phi):

are you confused how to switch between radical and exponent form?

OpenStudy (joftheworld):

yes..

OpenStudy (phi):

First, the two forms mean the same thing. if you have a radical sign with a little number "n" out front \[ \sqrt[n]{x} = x^\frac{1}{n} \] you can write it as the exponent 1/n If they don't show a little number n out front, it is assumed to be 2

OpenStudy (phi):

to switch from x^(1/n) you write \( \sqrt{x} \) in its place, and then put a little "n" out front: \( \sqrt[n]{x}\)

OpenStudy (phi):

\[ 4ab ^{3}\ a^{½} c ^{½} \] becomes \[ 4ab ^{3}\ \sqrt{a} \sqrt{ c} \] and we can combine the square roots \[ 4ab ^{3}\ \sqrt{ac} \]

OpenStudy (joftheworld):

so is that it ?

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