Answer:
25
Step-by-step explanation:
So basically remember that:
[tex](a+b)^2=a^2+2ab+b^2[/tex]
so far you have that
[tex]a^2 = x^2\\2ab = -10x[/tex]
So if 2ab = -10x and a = x, that means 2xb = -10x so b = -5.
It's kind of confusing to think of it like that, but all that means is that the equation is:
[tex](x - 5)^2[/tex]
which would simplify to
[tex]x^2 - 10x + 25[/tex]
so the blank is 25
