Answer:
25.
Step-by-step explanation:
If an expression is
[tex]x^2+bx[/tex]
then we have to add [tex](\frac{b}{2})^2[/tex], to make it perfect quare.
The given expression is
[tex]x^2+10x[/tex]
Here, b=10.
[tex](\frac{b}{2})^2=(\frac{10}{2})^2=5^2=25[/tex]
Now,
[tex]x^2+10x+25=x^2+2x(5)+5^2=(x+5)^2[/tex]
Therefore, we need to add 25 to make it perfect square.
