Bài 2 : Tìm x thuộc Z biết:
1) x-2=6
2) -5x-(-3)=13
3) 15- ( x-7 ) = -21
4) 3x+17 = 2
5) 45- (x-9)=-35
6) (-5)+x=15
7) 2x – (-17)=15
8) /x-2/=3
9)/x-3/-7=13
10) 72-3./x+1/=9
11) 17-( 43-/x/) = 45
12) 3 / x – 1 /-5 =7
13) -12 ( x-5 ) + 7 (3-x)=5
14) ( x-2 ) . ( x+4 ) = 0
15) ( x-2 ). ( x+15)= 0 .
16) ( 7-x ). ( x+19 )=0
17) -5 < x<1
18) /x/ <3
19) ( x-3 ) (x-5 )<0
20) 2x2-3=29
21) -6x - ( -7 ) = 25
22) 46- ( x-11 )= -48
Hộ mik vs
Đáp án + Giải thích các bước giải:
`1)` `x-2=6`
`x = 6 + 2`
`x = 8`
`2)` `-5x-(-3)=13`
`-5x + 3 = 13`
`-5x = 13 – 3`
`-5x = 10`
`x = 10 : (-5)`
`x = -2`
`3)` `15- ( x-7 ) = -21`
`x – 7 = 15 + 21`
`x – 7 = 36`
`x = 36 + 7`
`x = 43`
`4)` `3x+17 = 2`
`3x = 2 – 17 `
`3x = 2 + (-17)`
`3x = -15`
`x = -15 : 3`
`x = -5`
`5)` `45- (x-9)=-35`
`x – 9 = 45 + 35`
`x – 9 = 80`
`x = 80 + 9`
`x = 89`
`6)` `(-5)+x = 15`
`x = 15 + 5`
`x = 20`
`7)` `2x – (-17) = 15`
`2x + 17 = 15`
`2x = 15 – 17`
`2x = 15 + (-17)`
`2x = -2`
`x = -2 : 2`
`x = -1`
`8)` `|x-2| = 3`
`=> x – 2 = ± 3`
`+) x – 2 = 3`
`x = 3 + 2`
` x = 5`
`+) x – 2 = -3`
`x = -3 + 2`
`x = -1`
`=>` `x in {5;-1}`
`9)` `|x-3|-7=13`
`|x-3| = 13 + 7`
`|x-3| = 20`
`=> x – 3 = ±20`
`+) x – 3 = 20`
`x = 20 + 3`
`x = 23`
`+) x – 3 = -20`
`x = -20 + 3`
`x = -17`
`=> x in {23;-17}`
`10)` `72-3.|x+1|=9`
`3.|x+1| = 72 – 9`
`3.|x+1| = 63`
`|x+1| = 63 : 3`
`|x+1| = 21`
`=> x+ 1 = ± 21`
`+) x + 1 = 21`
`x = 21 – 1`
`x = 20`
`+) x + 1 = -21`
`x = -21 – 1`
`x = -21 + (-1)`
`x = -22`
`11)` `17-(43-|x|) = 45`
`43 – |x| = 17 – 45`
`43 – |x| = 17 + (-45)`
`43 – |x| = -28`
`|x| = 43 + 28`
`|x| = 71`
`=> x in {71;-71}`
`12)` `3|x – 1|-5 =7`
`3|x-1| = 7 + 5`
`3|x-1| = 12`
`|x-1| = 12 : 3`
`|x-1| = 4`
`=> x – 1 = ±4`
`+) x – 1 = 4`
`x = 4 + 1`
`x = 5`
`+) x – 1 = -4`
`x = -4 + 1`
`x = -3`
`=> x in {5;-3}`
`13)` `-12(x-5) + 7(3-x)=5`
`-12x – (-12).5 + 7.3 – 7x = 5` (Dùng tính chất phân phối của phép nhân đ/v phép cộng)
`-12x + 60 + 21 – 7x = 5`
`(-12x – 7x) + (60 + 21) = 5`
`-19x + 81 = 5`
`-19x = 5 – 81`
`-19x = -76`
`x = -76 : (-19)`
`x = 4
`14)` `( x-2 ) . ( x+4 ) = 0`
`=> x – 2 = 0` hoặc `x + 4 = 0`
`+) x – 2 = 0`
`x = 0 + 2`
`x = 2`
`+) x + 4 = 0`
`x = 0 – 4`
`x = -4`
`=> x in {2;-4}`
`15)` `( x-2 ). ( x+15)= 0 `
`=> x – 2 = 0` hoặc `x + 15 = 0`
`+) x – 2 = 0`
`x = 0 + 2`
`x = 2`
`+) x + 15 = 0`
`x = 0 – 15`
`x = -15`
`=> x in {2;-15}`
`16)` `(7-x ). ( x+19 )=0`
`=> 7-x = 0` hoặc `x + 19 = 0`
`+) 7 – x = 0`
`x = 7 – 0`
`x = 7`
`+) x + 19 = 0`
`x = 0 – 19`
` x = -19`
`=> x in {7;-19}`
`17)` `-5 < x<1`
`=> x in {-4;-3;-2;-1;0}`
`18)` `|x| <3`
`=> -3 < x < 3`
`=> x in {±2;±1;0}`
`19)` `( x-3 )(x-5 )< 0`
`=> x – 3` và `x – 5` trái dấu
Mà `x – 3 > x – 5` nên `x – 3 > 0` (nguyên dương), `x – 5 < 0` (nguyên âm)
`+) x – 3 > 0 => x > 3`
`+) x – 5 < 0 => x < 5`
Vậy `3 < x < 5;` `x in ZZ` `=> x = 4`
Vậy nên: `x = 4`
`20)` `2x^2-3=29`
`2x^2 – 3 = 29`
`2x^2 = 29 + 3`
`2x^2 = 32`
` x^2 = 32 : 2`
`x^2 = 16`
`=> x = ±4`
`21)` `-6x – ( -7 ) = 25`
`-6x + 7 = 25`
`-6x = 25 – 7`
`-6x = 18`
`x = 18 : (-6)`
`x = -3`
`22)` `46- ( x-11 )= -48`
`x – 11 = 46 – (-48)`
`x – 11 = 46 + 48`
`x – 11 = 94`
`x = 94 + 11`
`x = 105`
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