Question 766421
x^2 + 4x - 9
separate -9
x^2 + 4x ......-9
Halve the number before the x and square it
x^2 + 4x + (4/2)^2.......-9
x^2 + 4x + 4 ...........-9
Now because we have added +4
to the left hand side we must add -4 
to the -9
x^2 + 4x + 4.......-4 -9
This then is presented as:-
(x + 2)^2  - 13
Hope this helps.
:-)