-Tìm x;y;z E Q biết:
a)|x+13/7|+|y+2020/2019|+|z-2018|=0
b)|x-1/2|+|y+3/2|+|z-5/2|<0
-Tìm x;y;z E Q biết: a)|x+13/7|+|y+2020/2019|+|z-2018|=0 b)|x-1/2|+|y+3/2|+|z-5/2|<0
By Isabelle
By Isabelle
-Tìm x;y;z E Q biết:
a)|x+13/7|+|y+2020/2019|+|z-2018|=0
b)|x-1/2|+|y+3/2|+|z-5/2|<0
a, Do
`|x+13/7| ≥ 0 ; |y+2020/2019|≥0;|z-2018|≥0`
`=>|x+13/7|+|y+2020/2019|+|z-2018|≥0`
Do đó để `|x+13/7|+|y+2020/2019|+|z-2018|=0` thì
`x+13/7=y+2020/2019=z-2018=0`
`=> x = -13/7 ; y = -2020/1019 ; z = 2018`
b, Do
`|x-1/2|≥0;|y+3/2|≥0;|z-5/2|≥ 0`
`=> |x-1/2|+|y+3/2|+|z-5/2|≥0`
`=>|x-1/2|+|y+3/2|+|z-5/2|<0` (vô lí)
`=> x ; y ; z ∈ ∅`