ok you are right i forget 

-x-5=0

x=-5 i forget

his question is what is -(x-5)^2

but i also did =0

what is -(x-5)^2

-(x^2+5^2-2*x*-5)

-(x^2+5^2+10x)

-(x^2+10x+25)

-x^2-10x-25=0

-x^2-5x-5x-25=0

-x(x+5)-5(x+5)

(x+5)(-x-5)

x+5=0   ,      -x-5=0

x=-5      ,      x=5

x=+or-5

Thanks Mat

but there is no =0 in the question  

I assume the asker just wanted you to expand and simplify it.

Also, if it did equal 0 your answer is not correct.   The answer would simply be x-5=0  so  x=+5