Solving equations {(X-2) (y + 3) = (x + 1) (Y-1) {(x + 1) (y + 1) = (x-1) (y + 5)

Solving equations {(X-2) (y + 3) = (x + 1) (Y-1) {(x + 1) (y + 1) = (x-1) (y + 5)

{(x-2)(y+3)=(x+1)(y-1)
{(x+1)(y+1)=(x-1)(y+5)
{xy+3x-2y-6=xy-x+y-1
{xy+x+y+1=xy+5x-y-5
{4x-3y=5 (1)
{4x-2y=6 (2)
(1)+(2)
-y=-1
y=1
4x=5+3y
4x=5+3
4x=8
x=2
X = 2, y = - 1 of the equations

2011 * 1999 and 998 * 1002 are calculated by square difference
I'm not familiar with the process of these two questions..

2011 = 2010 + 11999 = 2010-1, so 2011 × 1999 = (2010 + 1) × (2010-1) = 2010 & # 178; - 1 & # 178; = 4040099 -------- 998 = 1000-21002 = 1000 + 2998x1002 = (1000-2) × (1000 + 2) = 1000 & # 178; - 2 & # 178; = 999996