773.1) 3+(x+y)+t=3+x+y+t;
2) 4+a-(b+c)=4+a-b-c;
3) n-(4-m+d)=n-4+m-d;
4)-(8+ z)+ (s - k)=-8-z+sk;
776.1)-(8¹/₃·a-9b)+7.5a-10¹/₇b=-(5/6a+1¹/₇b);⇒
-25/3a+9b+15/2a-71/7b=(-50+45)/6·a+(63-71)/7b=-5/6·a-8/7b=
=-(5/6a+1¹/₇b);
3)17¹³/₁₄·a-3¹/₇·b-(2.5a+5b)=3/7·(36a-19b);⇒
251/14·a-22/7b-5/2·a-5b=(251-35)/14·a-(22+35)/7b=216/14a-57/7b=
=108/7·a-57/7·b=3/7·(36a-19b);