Precalc project: positive values in an inequality

  • Thread starter hpdwnsn95
  • Start date
  • #1
6
0

Homework Statement


Determine the set of positive values of x that satisfy the following inequality:
(1/x) - (1/(x-1)) > (1/(x-2))

a) (0, 1) union (2^1/2, 2) b) (0, 1/2) union (1, 2) c) (1/2, 1) union (2^1/2, 2(2^1/2))
d) (0, 2^1/2) union (3/2, 2) e) (1, 2^1/2) union (2, 2(2^1/2))

Homework Equations


i'm not sure that there are any relevant equations, just started precalc a few weeks ago and i'm not sure how to solve the problem


The Attempt at a Solution


I've tried graphing the equation and then tracing x to find y, but I haven't been able to find an answer that way. I've also tried solving for x which i get 1/2 > x for, but I'm not sure if that applies to this problem
 
Last edited by a moderator:

Answers and Replies

  • #2
34,688
6,394

Homework Statement


Determine the set of positive values of x that satisfy the following inequality:
(1/x) - (1/(x-1)) > (1/(x-2))

a) (0, 1) union (2^1/2, 2) b) (0, 1/2) union (1, 2) c) (1/2, 1) union (2^1/2, 2(2^1/2))
d) (0, 2^1/2) union (3/2, 2) e) (1, 2^1/2) union (2, 2(2^1/2))

Homework Equations


i'm not sure that there are any relevant equations, just started precalc a few weeks ago and i'm not sure how to solve the problem


The Attempt at a Solution


I've tried graphing the equation and then tracing x to find y, but I haven't been able to find an answer that way. I've also tried solving for x which i get 1/2 > x for, but I'm not sure if that applies to this problem
The first step would be to combine the two fractions on the left side.
 
  • #3
PeterO
Homework Helper
2,426
48

Homework Statement


Determine the set of positive values of x that satisfy the following inequality:
(1/x) - (1/(x-1)) > (1/(x-2))

a) (0, 1) union (2^1/2, 2) b) (0, 1/2) union (1, 2) c) (1/2, 1) union (2^1/2, 2(2^1/2))
d) (0, 2^1/2) union (3/2, 2) e) (1, 2^1/2) union (2, 2(2^1/2))

Homework Equations


i'm not sure that there are any relevant equations, just started precalc a few weeks ago and i'm not sure how to solve the problem


The Attempt at a Solution


I've tried graphing the equation and then tracing x to find y, but I haven't been able to find an answer that way. I've also tried solving for x which i get 1/2 > x for, but I'm not sure if that applies to this problem
Is this actually a multiple choice question? Is that what the a) b) c) etc refer to ?
 
  • #5
PeterO
Homework Helper
2,426
48

Homework Statement


Determine the set of positive values of x that satisfy the following inequality:
(1/x) - (1/(x-1)) > (1/(x-2))

a) (0, 1) union (2^1/2, 2) b) (0, 1/2) union (1, 2) c) (1/2, 1) union (2^1/2, 2(2^1/2))
d) (0, 2^1/2) union (3/2, 2) e) (1, 2^1/2) union (2, 2(2^1/2))

Homework Equations


i'm not sure that there are any relevant equations, just started precalc a few weeks ago and i'm not sure how to solve the problem


The Attempt at a Solution


I've tried graphing the equation and then tracing x to find y, but I haven't been able to find an answer that way. I've also tried solving for x which i get 1/2 > x for, but I'm not sure if that applies to this problem
Remember that if this is a multiple choice question, you do not have to find the answer, you only have to identify which of the 5 offerings is the answer.

While not a great method of solving a problem, substituting the offerings into the original inequality may be the fastest way for you to solve this.
 
  • #6
symbolipoint
Homework Helper
Education Advisor
Gold Member
6,115
1,161

Homework Statement


Determine the set of positive values of x that satisfy the following inequality:
(1/x) - (1/(x-1)) > (1/(x-2))

a) (0, 1) union (2^1/2, 2) b) (0, 1/2) union (1, 2) c) (1/2, 1) union (2^1/2, 2(2^1/2))
d) (0, 2^1/2) union (3/2, 2) e) (1, 2^1/2) union (2, 2(2^1/2))

Homework Equations


i'm not sure that there are any relevant equations, just started precalc a few weeks ago and i'm not sure how to solve the problem


The Attempt at a Solution


I've tried graphing the equation and then tracing x to find y, but I haven't been able to find an answer that way. I've also tried solving for x which i get 1/2 > x for, but I'm not sure if that applies to this problem
If you do not know or see a clever trick to use, then solving the problem using basic principles is the best way. In the sample problem, start by adding the additive inverse of the righthand member to both sides; then perform the arithmetic steps for the rational expressions. You have some rational expression related to zero. Now just focus on the numerator.
 
  • #7
HallsofIvy
Science Advisor
Homework Helper
41,833
962
Given that x is positive, I would separate this problem into three parts:
x between 0 and 1: both x- 1 and x- 2 are negative.

x between 1 and 2: x- 1 is positive but x- 2 is negative

x greater than 2: both x- 1 and x- 2 are positive.

For each of those, multiply the entire inequality by x(x-1)(x-2).
 
  • #8
6
0
Is this actually a multiple choice question? Is that what the a) b) c) etc refer to ?
yes it is
 
  • #9
6
0
Remember that if this is a multiple choice question, you do not have to find the answer, you only have to identify which of the 5 offerings is the answer.

While not a great method of solving a problem, substituting the offerings into the original inequality may be the fastest way for you to solve this.
I would do that but I don't understand the answer format, i"ve never seen union answers before, can you (or anyone else) expain them?
 
  • #10
SammyS
Staff Emeritus
Science Advisor
Homework Helper
Gold Member
11,358
1,031
Do you know what the definition of the union of two sets is?
 
  • #11
6
0
Do you know what the definition of the union of two sets is?
i think union stands for and right? so it's like one set & one set
but i'm not sure how would plug either set into the problem because there's no y in the problem
 
  • #12
SammyS
Staff Emeritus
Science Advisor
Homework Helper
Gold Member
11,358
1,031
One piece (interval) of the x-axis plus (as in union) another piece. --- Actually, all the numbers in one interval together with all the numbers in another interval together with ...
 
  • #13
PeterO
Homework Helper
2,426
48
I would do that but I don't understand the answer format, i"ve never seen union answers before, can you (or anyone else) expain them?
The first option

(0, 1) union (2^1/2, 2)

suggests it is true for any value between 0 and 1, as well as values between √2 and 2, but false for values between 1 and √2, and false for values above 2
it is clearly undefined for x = 0,1 or2 due to a fraction becoming 1/0

You could substitute 0.5 [1/2], and check it is true, 1.25 [5/4] and check it is false, 1.5 [3/2] and check it is true and 3 to check it is false.

Solving is better, but substitution could be your last resort.
 

Related Threads on Precalc project: positive values in an inequality

  • Last Post
Replies
0
Views
2K
  • Last Post
Replies
1
Views
3K
  • Last Post
Replies
10
Views
2K
  • Last Post
Replies
15
Views
1K
  • Last Post
Replies
7
Views
2K
  • Last Post
Replies
5
Views
2K
  • Last Post
Replies
4
Views
1K
  • Last Post
Replies
5
Views
942
  • Last Post
Replies
2
Views
605
  • Last Post
Replies
3
Views
1K
Top