... x1.x 2 + x1.x 2 = x1. x 2 + x1(x 2 + x 2 ) = x1. x 2 + x1 = x1 + x 2 Vióỳt theo daỷng chờnh từc 2 ta coù: f(x1, x 2 ) = [0+x1+x 2 ].[1+x1+x 2 ].[1+x1+ x 2 ].[1+x1+x 2 ] ... f(0, x 2 ). x1 + f(1,x 2 ).x1maỡ: f(0, x 2 ) = f(0,0 ). x 2 + f(0,1).x 2 vaỡ: f(1, x 2 ) = f(1,0). x 2 + f(1,1). x 2 Suy ra: f(x1, x 2 ) = f(0,0) x1x 2 + f(0, 1) x1x 2 + f(1,0 ... 2: f(x1, x 2 , x3) = x1 + x 2 .x3 Viãút dỉåïi dảng chênh tàõc 2: f(x1, x 2 , x3) = [0+x1+x 2 +x3].[0+x1+x 2 +x3].[0+x1+x 2 +x3]. [1+x1+x 2 +x3].[1+x1+x 2 +x3].[1+x1+x 2 +x3]....