Bài 13:
a: \(-\dfrac{1}{2}=-\dfrac{2}{4}>-\dfrac{3}{4}\)
\(-\dfrac{3}{4}>-1>-\sqrt{2}\)
Do đó: 0>\(-\dfrac{1}{2}>-\dfrac{3}{4}>-\sqrt{2}\)(1)
\(0,\left(5\right)=\dfrac{5}{9}< 1;1< 2,78< 6\)
Do đó: \(0< 0,\left(5\right)< 2,78< 6\left(2\right)\)
Từ (1),(2) suy ra \(-\sqrt{2}< -\dfrac{3}{4}< -\dfrac{1}{2}< 0,\left(5\right)< 2,78< 6\)
b: \(\left|-\sqrt{2}\right|=\sqrt{2};\left|-\dfrac{3}{4}\right|=\dfrac{3}{4};\left|-\dfrac{1}{2}\right|=\dfrac{1}{2}\)
\(\left|0,\left(5\right)\right|=\dfrac{5}{9};\left|2,78\right|=2,78;\left|6\right|=6\)
Ta có: \(\dfrac{1}{2}=\dfrac{18}{36};\dfrac{3}{4}=\dfrac{27}{36};\dfrac{5}{9}=\dfrac{20}{36}\)
Do đó: \(\dfrac{18}{36}< \dfrac{20}{36}< \dfrac{27}{36}\)
=>\(\left|-\dfrac{1}{2}\right|< \left|0,\left(5\right)\right|< \left|-\dfrac{3}{4}\right|< 1\left(1\right)\)
\(1< \sqrt{2}< 2,78< 6\)
=>\(1< \left|-\sqrt{2}\right|< \left|2,78\right|< \left|6\right|\)(2)
Từ (1),(2) suy ra \(\left|-\dfrac{1}{2}\right|< \left|0,\left(5\right)\right|< \left|-\dfrac{3}{4}\right|< \left|-\sqrt{2}\right|< \left|2,78\right|< \left|6\right|\)
Bài 14:
x=-2,5 nên x<0
x+y=9,6
mà x<0
nên y>0
