Bài toán 3: Tìm x ∈ Z biết.
a) 5 – (12 – x) = 129 – (6 + 129)
b) 20 – (x + 3) = – 45 – (17 – 45)
c) 24 + (17 – x) = (125 – 30) – 125
d) k) 3(x – 4) – (8 – x) = 12
e) x – (13 – x) = – 24 + (-7 + x)
f) (x – 7) + (5 – x) = 12 – (-8 + x) k
g) 124 + (13 – 16) = 162 – (x + 162)
h) 5(x – 6) – 2(x + 3) = 12
Đáp án + Giải thích các bước giải:
Ta có :
`a,5-(12-x)=129-(6+129)`
`→5-12+x=129-129-6`
`→-7+x=-6`
`→x=1`
`b,20-(x+3)=-45-(17-45)`
`→20-x-3=-45+45-17`
`→17-x=-17`
`→x=34`
`c,24+(17-x)=(125-30)-125`
`→24+17-x=125-125-30`
`→41-x=-30`
`→x=71`
`k,3(x-4)-(8-x)=12`
`→3x-12-8+x=12`
`→4x-20=12`
`→4x=32`
`→x=8`
`e,x-(13-x)=-24+(-7+x)`
`→x-13+x=-24-7+x`
`→2x-13=-31+x`
`→2x-x=13-31`
`→x=-18`
`f,(x-7)+(5-x)=12-(-8+x)`
`→x-7+5-x=12+8-x`
`→-2=20-x`
`→x=2+20`
`→x=22`
`g,124+(13-16)=162-(x+162)`
`→124+13-16=162-162-x`
`→121=-x`
`→x=-121`
`h,5(x-6)-2(x+3)=12`
`→5x-30-2x-6=12`
`→3x-36=12`
`→3x=48`
`→x=16`
Bài toán 3 :
a) 5 – (12 – x) = 129 – (6 + 129)
<=> 5 – 12 + x = 129 – 6 – 129
<=> x = 129 – 6 – 129 – 5 + 12
<=> x = 1
b) 20 – (x + 3) = – 45 – (17 – 45)
<=> 20 – x – 3 = -45 – 17 + 45
<=> -x = -45 – 17 + 45 + 3 – 20
<=> -x = -34
<=> x = 34
c) 24 + (17 – x) = (125 – 30) – 125
<=> 24 + 17 – x = 95 – 125
<=> -x = 95 – 125 – 17 – 24
<=> -x = -71
<=> x = 71
d) 3(x – 4) – (8 – x) = 12
<=> 3x – 12 – 8 + x = 12
<=> 3x + x = 12 + 8 + 12
<=> 4x = 32
<=> x = 8
e) x – (13 – x) = – 24 + (-7 + x)
<=> x – 13 + x = -24 – 7 + x
<=> x + x – x = -24 -7 + 13
<=> x = -18
f) (x – 7) + (5 – x) = 12 – (-8 + x)
<=> x – 7 + 5 – x = 12 + 8 – x
<=> x – x + x = 12 + 8 + 7 – 5
<=> x = 22
g) 124 + (13 – 16) = 162 – (x + 162)
<=> 124 + 13 – 16 = 162 – x – 162
<=> x = 162 – 162 – 124 – 13 + 16
<=> x = -121
h) 5(x – 6) – 2(x + 3) = 12
<=> 5x – 30 – 2x – 6 = 12
<=> 5x – 2x = 12 + 6 + 30
<=> 3x = 48
<=> x = 16