Addmath!!!!

F(x) =-x^2+4x+5----------1

=-(x^2-4x-5)----------2

=-[x^2-4x+(-4/2 )^2-( -4/2 )^2 -5]----------3

=-(x-2)^2 +9----------4

weh!! cam ne nk dapatkan langkah ke-3??
anyone who can explain this?? msg aku erk at fb!! thx..mmmuah (^_^)