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Mathematics 8 Online
OpenStudy (ltrout):

What is the solution of the equation?

OpenStudy (ltrout):

\[4(3-x)^{\frac{ 4 }{ 3 }-5}=59\]

OpenStudy (maddy1251):

Alright. Do you want to try it on your own first, and see if you can get an answer?

OpenStudy (ltrout):

Sure, I'll write it down on paper because solving math on here isn't the easiest.

OpenStudy (maddy1251):

I agree. You go ahead and try it, if you cannot get it, we will walk through step by step :) No rush

OpenStudy (maddy1251):

Maybe I will start writing the steps, because I might have to leave and get pizza in a few. xD

OpenStudy (maddy1251):

What we are going to do is take 4(3-x)^4/3 - 5 = 59 . Lets add that (-5) to both sides to get; 4(3-x)^4/3 = 64

OpenStudy (maddy1251):

From here, we will try to remove the "4" so we will have -- > (3-x)^4/3 instead. So lets divide 4 from each side. We will then have (3-x)^4/3 = 16

OpenStudy (maddy1251):

Now we use the principle of fraction exponents to radicals

OpenStudy (maddy1251):

A^B/C = c(sqrt(a))^B

OpenStudy (maddy1251):

\[\sqrt[3]{3-x}^{4} = 16\]

OpenStudy (maddy1251):

We use the principle of even roots, in this case 4th roots. When taking even roots we must use ± on the right side. Now since 16 = 2·2·2·2 = 24, then the 4th root of 16 is 2. So we have:

OpenStudy (maddy1251):

\[\sqrt[3]{3-x} = \pm 2\]

OpenStudy (maddy1251):

Next to get rid of the cube root we cube both sides........

OpenStudy (maddy1251):

(Simply distribute it)

OpenStudy (maddy1251):

3-x = ± 8

OpenStudy (maddy1251):

If we use the " + " we get; 3-x = 8 -x = 5 x = -5

OpenStudy (maddy1251):

If we use the - we get 3-x = -8 -x = -11 x = 11

OpenStudy (maddy1251):

Both are valid solutions, when put into the original equation.

OpenStudy (maddy1251):

Just put them where 'x' is to check, if you are unsure.

OpenStudy (maddy1251):

Sorry if it was messy or rushed, I had to kind of hurry. xD I wanted to make sure you had the answer in time.

OpenStudy (ltrout):

No, that's fine! That makes sense now. Question, when you cubed both sides, why did you drop the exponent of 4?

OpenStudy (maddy1251):

Because of this...: We use the principle of even roots, in this case 4th roots. When taking even roots we must use ± on the right side. Now since 16 = 2·2·2·2 = 24, then the 4th root of 16 is 2. So we have:\[\sqrt[3]{3-x} = \pm 2\] By taking the 16 and doing .... 2 x 2 x 2 x 2 = 2^{4} this sort of cancels it out, I guess

OpenStudy (ltrout):

Okay, makes sense. Thank you so much! :)):):):):):):)

OpenStudy (maddy1251):

Not a problem, if you have any more questions, please feel free to tag me!

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