X2+X2 =

Here the given expression, 

$X2 + X\mathrm{2 }$ is an algebraic expression. Here in this expression the terms are like terms. Now to add them, add their coefficients.

Here in the given expression, the like terms are two  $X\mathrm{2 }$

Hence, adding their coefficients i.e, 1 + 1 = 2

Therefore, 

$X2 + X2$ = 2 $X2$.