Question

x2 + 2005x – 2006 = 0

Answer 1

Д=2007^2
х1= (-2005+2007)/2=1
х2=(-2005-2007)/2=-2006

Answer 2

D = 2005^2 + 4*2006 = 2005^2 + 4*(2005+1) = 2005^2 + 2*2*2005 + 2^2 = 
(2005+2)^2 = 2007^2
(x)1;2= (-2005 +- 2007) / 2
x1 = (-2005-2007)/2 = (-2005-2005-2)/2 = (-2*2005 - 2)/2 = -2005-1 = -2006
x2 = (-2005+2007)/2 = 2/2 = 1