(x+2)^2-(y-3)^2=(x+y)(x-y)...( 1)

x-3y=2...(2)

X=3y+2...(3) From (2), substitute (3) into (1) to get:

(3y+4) 2-(y-3) 2 = (4y+2) (2y+2), the solution is:

y=- 1/6...(4),

Substitution into (2) gives:

x=3/2

2. 1

(X-Y)^2

=X^2+2XY+Y^2-4XY

=(X+Y)^2-4XY

=49/36-4XY

=625/36XY

=-4

So XY+4=-4+4=0.

2.2

a-b=2，b-c=-3，c-d=5

a-c=(a-b)+(b-c)=2-3=- 1

b-c=(b-c)+(c-d)=-3+5=2

a-d=(a-b)+(b-c)+(c-d)=2-3+5=4

therefore

(a-c)(b-d)/(a-d)=- 1/2