1.
-(x+y) = 1/3-0,5= 1/3-5/10=10/30-15/30=-5/30
-(x-y)=1/3+0,5=10/30+15/30=25/30
-(-x+y)=-1/3-0,5=-10/30-15/30=-25/30
-(-x-y) =-1,3+0,5=-10/30+15/30=5/30
2
(a+c)(a-c)=(0,2-0,6)(0,2+0,6)=(2/10-6/10)(2/10+6/10)=-4/10*8/10=-32/10=-3(целых).2/10=-3.1/5
a+c/a-c=2,5-1/2,5+1=1,5/3,5