Question

What number should be added to the expression x^2 + 4x to change it into a perfect square trinomial?

Answer 1

X^2 + 4x
the number to be added is found by dividing the constant of x by 2
 and squared the number
so # to be added =  ( 4/2)²  =  4
the perfect square trinomial is
x² + 4x + 4    =    (x + 2 )²    which is a perfect square trinomial
I hope this help you

Answer 2

He number that must be added is four because (x+2)^2=x^2+4x+4