Determine whether the equations are identities or not.

? Identity Not an identity  1. $x^2 + 2 = 3x$

? Identity Not an identity  2. $2x^2 + 3x^2 = 5x^2$

? Identity Not an identity  3. $2u^2 + 3u^3 = 5u^5$

? Identity Not an identity  4. $t + 1/(t^2+1) = (t+1)/(t^2+1)$