Question 819482
x^2 -10x = -24 
is fine
x^2 -10x +24 =0
find factors of 24 that add up to -10
-6 and -4
(x-6)*(x-4)=0
x=6 x=4
check
36-60=-24
16-40=-24
ok

but that is not completing the square.
x^2 -10x = -24 
x^2 -10x +25= 1
(x-5)^2=1
x-5=+-1
x=6
x=4