Bài 4
l) 4(x – 5) – 3(x + 7) = -19
k) 7(x – 3) – 5(3 – x) = 11x – 5
l) 7(x – 9) – 5(6 – x) = -6 + 11x
a. 5x – 16 = 40 + x
b. 4x – 10 = 15 – x
c. -12 + x = 5x – 20
d. 7x – 4 = 20 + 3x
e. 5x – 7 = – 21 – 2x
f. x + 15 = 7 – 6x
g. 17 – x = 7 – 6x
h. 3x + (-21) = 12 – 8x
Đáp án:
Giải thích các bước giải:
l) 4(x – 5) – 3(x + 7) = -19
↔ 4x – 20 – 3x – 21 = -19
↔ x – 41 = -19
↔ x = -19 + 41
↔ x = 22
Vậy x = 22
k) 7(x – 3) – 5(3 – x) = 11x – 5
↔ 7x – 21 – 15 + 5x = 11x – 5
↔ 7x + 5x – 11x = -5 + 21 + 15
↔ x = 31
Vậy x = 31
l) 7(x – 9) – 5(6 – x) = -6 + 11x
↔ 7x – 63 -30 + 5x = -6 + 11x
↔ 7x + 5x – 11x = -6 + 63 + 30
↔ x = 87
Vậy x = 87
a. 5x – 16 = 40 + x
↔ 5x – x = 40 + 16
↔ 4x = 56
↔ x = 14
Vậy x = 14
b. 4x – 10 = 15 – x
↔ 4x + x = 15 + 10
↔ 5x = 25
↔ x = 5
Vậy x = 5
c. -12 + x = 5x – 20
↔ x – 5x = -20 + 12
↔ -4x = -8
↔ x = 2
Vậy x = 2
d. 7x – 4 = 20 + 3x
↔ 7x – 3x = 20 + 4
↔ 4x = 24
↔ x = 6
Vậy x = 6
e. 5x – 7 = – 21 – 2x
↔ 5x + 2x = -21 + 7
↔ 7x = -14
↔ x = -2
Vậy x = -2
f. x + 15 = 7 – 6x
↔ x + 6x = 7 – 15
↔ 7x = -8
↔ x = -$\frac{8}{7}$
Vậy x = -$\frac{8}{7}$
g. 17 – x = 7 – 6x
↔ -x + 6x = 7 – 17
↔ 5x = 10
↔ x = 2
Vậy x = 2
h. 3x + (-21) = 12 – 8x
↔ 3x + 8x = 12 + 21
↔ 11x = 33
↔ x = 3
Vậy x = 3
`l) 4(x – 5) – 3(x + 7) = -19`
`<=> 4x – 20 – 3x – 21 = -19`
`<=> x – 41 = -19`
`<=> x = -19 + 41`
`<=> x = 22`
`—————`
`k) 7(x – 3) – 5(3 – x) = 11x – 5`
`<=> 7x – 21 – 15 + 5x = 11x – 5`
`<=>7x + 5x – 11x = -5 + 21 + 15`
`<=> x = 31 `
`—————`
`l) 7(x – 9) – 5(6 – x) = -6 + 11x`
`<=> 7x – 63 -30 + 5x = -6 + 11x`
`<=>7x + 5x – 11x = -6 + 63 + 30`
`<=> x = 87`
`—————`
`a) 5x – 16 = 40 + x`
`<=> 5x – x = 40 + 16`
`<=> 4x = 56`
`<=> x = 14`
`—————`
`b) 4x – 10 = 15 – x`
`<=> 4x + x = 15 + 10`
`<=> 5x = 25`
`<=> x = 5`
`—————`
`c) -12 + x = 5x – 20`
`<=> x – 5x = -20 + 12`
`<=> -4x = -8`
`<=> x = 2`
`—————`
`d) 7x – 4 = 20 + 3x`
`<=> 7x – 3x = 20 + 4 `
`<=> 4x = 24`
`<=> x = 6`
`—————`
`e) 5x – 7 = – 21 – 2x`
`<=> 5x + 2x = -21 + 7`
`<=> 7x = -14`
`<=> x = -2`
`—————`
`f)x + 15 = 7 – 6x`
`<=> x + 6x = 7 – 15`
`<=> 7x = -8`
`<=> x = –8/7 `
`—————`
`g) 17 – x = 7 – 6x`
`<=> -x + 6x = 7 – 17`
`<=> 5x = 10`
`<=> x = 2`
`—————`
`h) 3x + (-21) = 12 – 8x`
`<=> 3x + 8x = 12 + 21`
`<=> 11x = 33`
`<=> x = 3`