Ответ:

1. Переменные а, в, с

F(a, b, c) =a∧b∧c∨a∧¬b∧¬c∨¬a∧b∧¬c∨¬a∧¬b∧c

2.

F(a, b, c) = ¬a∧¬b∧¬c∨¬a∧b∧c∨a∧¬b∧c∨a∧b∧¬c

3.

F(X1,X2, X3, X4) =¬X1∧¬X2∧¬X3∧¬X4∨¬X1∧X2∧¬X3∧X4∨¬X1∧X2∧X3∧¬X4∨¬X1∧X2∧X3∧X4∨X1∧¬X2∧X3∧¬X4∨X1∧X2∧X3∧¬X4