a) Ta có : \(1 < 2 \Rightarrow \sqrt 1 < \sqrt 2 \Rightarrow 1 < \sqrt 2 \)
Suy ra : \(1 + 1 < \sqrt 2 + 1\)
Vậy \(2 < \sqrt 2 + 1.\)
b) Ta có: \(4 > 3 \Rightarrow \sqrt 4 > \sqrt 3 \Rightarrow 2 > \sqrt 3 \)
Suy ra: \(2 - 1 > \sqrt 3 - 1\)
Vậy \(1 > \sqrt 3 - 1.\)
c) Ta có : \(31 > 25 \Rightarrow \sqrt {31} > \sqrt {25} \Rightarrow \sqrt {31} > 5\)
Suy ra: \(2.\sqrt {31} > 2.5\)
Vậy \(2\sqrt {31} > 10.\)
d) Ta có: \(11 < 16 \Rightarrow \sqrt {11} < \sqrt {16} \Rightarrow \sqrt {11} < 4\)
Suy ra: \( - 3.\sqrt {11} > - 3.4\)
Vậy \( - 3\sqrt {11} > - 12.\)
