Posted by **Samantha** on Thursday, June 4, 2009 at 8:53pm.

Which equation is an identity?

a. 3x - 9 = 3x

b. 4p + 7 = 7 + 4p

c. 2w = 0

d. 5k = 5

- ALSO... -
**Samantha**, Thursday, June 4, 2009 at 8:54pm
What's an identity?

- Math (Algebra/Pre-Algebra) -
**Reiny**, Thursday, June 4, 2009 at 9:01pm
an identity is an equation which is true for all values of the variable

As a quick test, if you solve it, and you get a true statement, then it is an identity.

e.g. look at the first answer

3x - 9 = 3x

-9 = 0, which is NOT true, so Not an identity

but

4p + 7 = 7 + 4p

solving this we get

0 = 0 which is TRUE, so it is an identity.

- Math (Algebra/Pre-Algebra) -
**Samantha**, Thursday, June 4, 2009 at 9:03pm
That makes so much sense! Thank you sooooooooo much! =]

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