Toán Lớp 7: Tìm x
2| 2x – 3 | = 1/2
7,5 – 3 | 5 – 2x | = – 4,5
| 3x – 4 | + | 3y – 5 | = 0
Leave a reply
Register Now
Login
Lost Password
Lost your password? Please enter your email address. You will receive a link and will create a new password via email.
Toán Lớp 7: Tìm x
2| 2x – 3 | = 1/2
7,5 – 3 | 5 – 2x | = – 4,5
| 3x – 4 | + | 3y – 5 | = 0
Comments ( 2 )
2.|2x-3|=1/2
=>|2x-3|=1/2:2
=>|2x-3|=1/2 . 1/2
=>|2x-3|=1/4
=>[(2x-3=1/4),(2x-3=-1/4):}
=>[(2x=1/4+3),(2x=-1/4+3):}
=>[(2x=1/4+12/4),(2x=-1/4+12/4):}
=>[(2x=13/4),(2x=11/4):}
=>[(x=13/4:2),(x=11/4:2):}
=>[(x=13/4 . 1/2),(x=11/4 . 1/2):}
=>[(x=13/8),(x=11/8):}
Vậy x\in{13/8;11/8}
b)
7,5-3|5-2x|=-4,5
=>3|5-2x|=7,5+4,5
=>3|5-2x|=12
=>|5-2x|=12:3
=>|5-2x|=4
=>[(5-2x=4),(5-2x=-4):}
=>[(2x=5-4),(2x=5+4):}
=>[(2x=1),(2x=9):}
=>[(x=1/2),(x=9/2):}
Vậy x\in{1/2;9/2}
c)
|3x-4|+|3y-5|=0
Ta có:
{(|3x-4|ge0 AAx),(|3y-5|ge0 AAy):}
=>|3x-4|+|3y-5|ge0 AAx;y
Mà |3x-4|+|3y-5|=0
=>{(|3x-4|=0),(|3y-5|=0):}
=>{(3x-4=0),(3y-5=0):}
=>{(3x=0+4),(3y=0+5):}
=>{(3x=4),(3y=5):}
=>{(x=4/3),(y=5/3):}
Vậy x=4/3;y=5/3