Math (Algebra/PreAlgebra)
posted by Samantha .
Which equation is an identity?
a. 3x  9 = 3x
b. 4p + 7 = 7 + 4p
c. 2w = 0
d. 5k = 5

What's an identity?

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