1.
57²+55²-110*57=57²+55²-2*55*57=(57-55)²=4
2.
a-b=(2010x+2008)-(2010x+2009)=-1
b-c=(2010x+2009)-(2010x+2010)=-1
a-c=(2010x+2008)-(2010x+2010)=-2
a²+b²+c²-ab-bc-ca=[(a-b)²+(b-c)²+(c-a)²]/2=3
3.
c=5,a+b+c=12
a²+b²=c²
S=ab/2=6
4.
y(x+y)+(x+y)(x-y)-x²
=x(x+y)-x²
=xy