\[\boxed{\text{1140.\ }\text{еуроки}\text{-}\text{ответы}\text{\ }\text{на}\text{\ }\text{пятёрку}}\]
\[x = 2,7.\]
\[\lbrack x\rbrack = \lbrack 2,7\rbrack = 2.\]
\[2\lbrack x\rbrack = 4.\]
\[\lbrack 2x\rbrack = \lbrack 5,4\rbrack = 5.\]
\[\lbrack - 2x\rbrack = \lbrack - 5,4\rbrack = - 6.\]