# Math (Algebra/Pre-Algebra)

posted by .

Which equation is an identity?

a. 3x - 9 = 3x
b. 4p + 7 = 7 + 4p
c. 2w = 0
d. 5k = 5

• ALSO... -

What's an identity?

• Math (Algebra/Pre-Algebra) -

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) -

That makes so much sense! Thank you sooooooooo much! =]

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