SOLUTION: what is the cube root of 72x^15y^15 divided by 27x^8y^7?

Algebra ->  Polynomials-and-rational-expressions -> SOLUTION: what is the cube root of 72x^15y^15 divided by 27x^8y^7?      Log On


   



Question 762443: what is the cube root of 72x^15y^15 divided by 27x^8y^7?
Found 2 solutions by Edwin McCravy, AnlytcPhil:
Answer by Edwin McCravy(20060) About Me  (Show Source):
You can put this solution on YOUR website!
I can't tell whether you mean:

root%283%2C%2872x%5E15y%5E15%29%2F%2827x%5E8y%5E7%29%29 or root%283%2C%2872x%5E15y%5E15%29%29%2F%2827x%5E8y%5E7%29

I'll assume it's the first way:

Divide 72, and 27 both by 9:



root%283%2C%288x%5E15y%5E15%29%2F%283x%5E8y%5E7%29%29

Subtract the exponents of x, 15-8 = 7
Subtract the exponents of y, 15-7 = 8

root%283%2C%288x%5E7y%5E8%29%2F3%29

Rationalize the denominator by multiplyin under the radical by 3%5E2%2F3%5E2
to make a perfect cube on the bottom:

root%283%2C%28expr%288x%5E7y%5E8%29%2F3%29%2Aexpr%283%5E2%2F3%5E2%29%29

root%283%2C%288%2A3%5E2x%5E7y%5E8%29%2F3%5E3%29 

Take cube roots of numerator and denominator:

root%283%2C8%2A3%5E2x%5E7y%5E8%29%2Froot%283%2C3%5E3%29

Take the cube root of 8 out in front of the radical 
on top as a 2:
Take the cube root of 3³on the bottom which is just 3

%282%2Aroot%283%2C3%5E2x%5E7y%5E8%29%29%2F3%29

Write 3² as 9 since the exponent 2 is less than the index of
the cube root which is 3.
Write the exponent 7 in terms of the largest multiple of the 
root index 3 which does not exceed it. 7=6+1
Write the exponent 8 in terms of the largest multiple of the 
root index 3 which does not exceed it. 8=6+2 
 
%282%2Aroot%283%2C9x%5E%286%2B1%29y%5E%286%2B2%29%29%29%2F3%29 

Write x6+1 as x6x1
Write y6+2 as y6y2

%282%2Aroot%283%2C9x%5E6x%5E1y%5E6y%5E2%29%29%2F3%29

Take x6 out in front as x2 by dividing
the exponent 6 by the index of the root, 3, getting  x2 

Take y6 out in front as y2 by dividing
the exponent 6 by the index of the root, 3, getting  y2

Drop the 1 exponent of the x

%282x%5E2y%5E2%2Aroot%283%2C9xy%5E2%29%29%2F3%29

You can leave it like that, or you can take the 2 on top and the
3 on the bottom and make a fraction 2%2F3 and write it like this:

2%2F3x²y²∛9xy²

Edwin

Answer by AnlytcPhil(1807) About Me  (Show Source):
You can put this solution on YOUR website!
I can't tell whether you mean:

root%283%2C%2872x%5E15y%5E15%29%2F%2827x%5E8y%5E7%29%29 or root%283%2C%2872x%5E15y%5E15%29%29%2F%2827x%5E8y%5E7%29

I'll assume it's the second way:

Divide 72, and 27 both by 9:

root%283%2C72x%5E15y%5E15%29%2F%2827x%5E8y%5E7%29

Write 72 as 8*9

root%283%2C8%2A9x%5E15y%5E15%29%2F%2827x%5E8y%5E7%29

Take the cube root of 8 out front as 2
Divide the exponents 15 by the root index 3,
and take them out front:

2x%5E5y%5E5%2Aroot%283%2C9%29%2F%2827x%5E8y%5E7%29

Subtract exponents of x and y and since the larger
exponents are on the bottom, put the result on the bottom:

2%2Aroot%283%2C9%29%2F%2827x%5E3y%5E2%29

Edwin