What makes an equation equivalent to another?

  • Context: High School 
  • Thread starter Thread starter Atran
  • Start date Start date
  • Tags Tags
    Equivalent
Click For Summary

Discussion Overview

The discussion revolves around the concept of equivalent equations in the context of linear equations and their graphical representations. Participants explore the criteria for determining when two equations represent the same line or have the same solution set, with examples provided for clarification.

Discussion Character

  • Conceptual clarification
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants assert that two equations are equivalent if they share the same solution set, meaning that every solution of one equation is also a solution of the other.
  • One participant suggests that the equations x + y = 32 and 2x + 2y = 64 are equivalent because they represent the same line, as each solution of the first equation is also a solution of the second.
  • Another participant argues that the first pair of equations (x + y = 32 and 3x + 2y = 70) are not equivalent since they represent distinct lines, although they intersect at a point.
  • There is a mention of two ways of thinking about the equations: one focusing on the existence of a single solution and the other on the equivalence of equations that share the same set of coordinates.
  • One participant provides a mathematical proof approach to show that x + y = 32 and 2x + 2y = 64 are equivalent by demonstrating that each is a subset of the other’s solution set.

Areas of Agreement / Disagreement

Participants generally agree on the definition of equivalent equations as those sharing the same solution set. However, there is disagreement regarding the equivalence of specific pairs of equations, particularly the first pair discussed, which some participants claim are distinct while others assert they are equivalent.

Contextual Notes

The discussion reflects varying interpretations of equivalence in the context of linear equations and the conditions under which equations can be considered equivalent. There are unresolved aspects regarding the graphical representation of the equations and the implications of their intersections.

Atran
Messages
93
Reaction score
1
I know that this is basic, but I don't get it. Say we have the system,
x + y = 32
3x + 2y = 70
Each equation represents a graph, and the solution is the point where the two lines intersect.

Here is where I am confused:
x + y = 32
2x + 2y = 64
What is the proof that the two equations are equivalent / represent the same graph?

I read that two equations are equivalent if they share the same implication:
Equivalent equations are ones such that the truth of one implies and is implied by the truth of the other.

Thanks for help.
 
Mathematics news on Phys.org
Start by saying that the two equations represent two distinct lines.

What can you conclude from that?
 
Atran said:
I know that this is basic, but I don't get it. Say we have the system,
x + y = 32
3x + 2y = 70
Each equation represents a graph, and the solution is the point where the two lines intersect.

Here is where I am confused:
x + y = 32
2x + 2y = 64
What is the proof that the two equations are equivalent / represent the same graph?

I read that two equations are equivalent if they share the same implication:
Equivalent equations are ones such that the truth of one implies and is implied by the truth of the other.

Thanks for help.

Equivalent equations have the same solution set.

Your first two equations are not equivalent, since their graphs are different. They do intersect at a point, though. Assuming that they intersect at (2, 3), the equations x = 2 and y = 3 would be equivalent to the first pair of equations you have above. (Note that I just made up a solution, so my equations x = 2 and y = 3 aren't actually equivalent to yours.)

For your second system of equations, both equations represent exactly the same line. Each solution of the first equation is also a solution of the second equation. In different words, if (x0, y0) is a solution (i.e., makes the equation a true statement) of the first equation, it will also be a solution of the second equation. For this example, the two equations are equivalent.
 
So there are two ways of thinking:

1) If the two equations have one solution (which is one pair (xi, yi)) then I treat x and y in the equations as two (different) values.
x+y=32
3x+2y=70

2x+2y=64
3x+2y=70

(3x+2y) - (2x+2y) = 70 - 64
x = 6 and y = 26

2) (x+y=32) is equivalent to (2x+2y=64), since they share the same set of coordinates, therefore the same graph. Let's say set A has the coordinates of (x+y=32), and set B of (3x+2y=70). The solution is the set, A \cap B.
 
Two equations are equivalent if they have exactly the same solution set. If (x, y) is in the solution set of the first equation then x+ y= 32. Multiplying both sides of the equation by 2, 2x+ 2y= 64 so (x, y) is in the solution set for that equation. That proves that the solution set for x+ y= 32 is a subset of the solution set for 2x+ 2y= 64. Now we have to do it the other way: if (x, y) is in the solution set for 2x+ 2y= 64, then they satisfy that equation. Dividing both sides by 2, x+ y= 32 so (x, y) is also in the solution set for that equaton and the solution set for 2x+ 2y= 64 is a subset of the solution set for x+ y= 32. Since each is a subset of the other, they are equal and the two equations are equivalent.
 

Similar threads

  • · Replies 9 ·
Replies
9
Views
2K
  • · Replies 8 ·
Replies
8
Views
3K
  • · Replies 15 ·
Replies
15
Views
3K
  • · Replies 6 ·
Replies
6
Views
3K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 5 ·
Replies
5
Views
3K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 18 ·
Replies
18
Views
5K
  • · Replies 10 ·
Replies
10
Views
3K
  • · Replies 5 ·
Replies
5
Views
2K