SOLUTION: Solve the problem 20/3n+1 - 4/3n-1 = 3/2.

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Question 72722This question is from textbook Algebra:Structure and Method
: Solve the problem 20/3n+1 - 4/3n-1 = 3/2. This question is from textbook Algebra:Structure and Method

Answer by rmromero(383)   (Show Source): You can put this solution on YOUR website!

Solve the problem
20 4
____ - ____ = 3/2
3n+1 3n-1
Find the LCD of 3n + 1 nd 3n - 1
LCD = (3n + 1)(3n - 1)
Multiply the LCD both sides
20 4
[(3n + 1)(3n - 1)] ____ - ____ = 3/2 [(3n + 1)(3n - 1)]
3n+1 3n-1
20 (3n - 1) - 4(3n + 1) = 3/2 (3n + 1)(3n - 1)
Simplify:
[20(3n) - 20 (1)] - [4(3n) + 4(1)] = 3/2(9n^2 - 1)

48n - 24 = (27/2)n^2 - 3/2

Multiply 2 both sides
96n - 48 = 27n^2 - 3
0 = 27n^2 - 96n + 45

Factor
0 = (9n - 5)(3n - 9)
Apply zero product property
9n - 5 = 0 and 3n - 9 = 0
9n = 5 3n = 9
n = 5/9 n = 3

If you want to see if the values of your n are correct,
substitute n = 5/9 and n = 3 to the equation.

Checking
20 4
____ - ____ = 3/2
3n+1 3n-1
When n = 5/9
20 4
________ - ________ = 3/2
3(5/9)+1 3(5/9)-1

20 4
_____ - ______ = 3/2
5/3+1 5/3-1
20 4
____ - ____ = 3/2
8/3 2/3

20*3 4*3
______ - _____ = 3/2
8 2
60 12 3
_____ - ___ = ____
8 2 2
30 3
____ - 6 = ___
4 2
30 24 3
____ - ___ = ___
4 4 2
6 3
___ = ___
4 2
3/2 = 3/2 ------> True
When n = 3
20 4
____ - ______ = 3/2
3(3)+1 3(3)-1

20 4
____ - ______ = 3/2
9 + 1 9 -1

20 4
____ - ______ = 3/2
10 8
2 - 1/2 = 3/2
4 1
___ - ___ = 3/2
2 2
3/2 = 3/2 ------> True


Therefore the solutions are n = 5/9 and n = 3
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