How do you distinguish between an identity and an equation?

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Discussion Overview

The discussion revolves around distinguishing between identities and equations in mathematics. Participants explore the definitions, implications, and contexts in which these terms are used, including examples from algebra and geometry.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Mathematical reasoning

Main Points Raised

  • Some participants suggest that an equation becomes an identity when it holds true for all values of the variables involved, while others argue that equations can be conditional, true only for specific values.
  • One participant notes that functions are not identities, as functions produce outputs based on inputs, whereas identities are statements that can be universally applied.
  • There is a discussion about the use of symbols like "≡" to denote identities, with examples provided to illustrate when an equation can be considered an identity.
  • Several participants debate the nature of statements in mathematics, with some asserting that identities are stronger statements than equations, while others challenge this view by discussing conditional equations.
  • Examples such as the equation of the sum of angles in a triangle and the equation 1/2 + 1/2 = 1 are used to illustrate the nuances between identities and equations, with differing interpretations presented.
  • One participant emphasizes the importance of context in determining whether a statement is an identity or an equation, suggesting that additional context can change the interpretation of mathematical statements.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the definitions and distinctions between identities and equations. Multiple competing views remain, with some arguing for a clear differentiation while others suggest that the definitions can overlap depending on context.

Contextual Notes

Participants express varying interpretations of mathematical terms based on different contexts, leading to potential ambiguities in definitions. The discussion highlights the complexity of mathematical language and the importance of context in understanding statements.

  • #31


tahayassen said:
If ≡ was replaced with =, wouldn't it also be true that the coefficients of their respective terms are equal?

No, because the two equations would have different meanings. Let's look at the equation in my example a couple of posts ago.

As an identity:
2 ##\equiv## (A + B)x + A

As an identity, the equation above has to be true for all values of x. In my previous work I solved for the constants A and B, and found them to be A = 2, B = -2.

As an ordinary equation:
2 = (A + B)x + A
If we interpret the above as an ordinary equation (not an identity), given values of A and B, we could solve for the value of x that makes the equation a true statement.

The work would look like this.
2 - A = (A + B)x
$$\Rightarrow x = \frac{2 - A}{A + B}$$
If someone tells us the values of the constants A and B, we can determine the value of x.
 

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