Bài 4:
1, $55 – 5(x + 3) = 8$
$⇔ 55 - 5x - 15 = 8$
$⇔ 70 - 5x = 8$
$⇔ 5x = 62$
$⇔ x = 62 : 5$
$⇔ x = \frac {62}{5} = 12,4$
2, $175 – 5(x + 3) = 85$
$⇔ 175 - 5x - 15 = 85$
$⇔ 160 - 5x = 85$
$⇔ 5x = 75$
$⇔ x = 75 : 5$
$⇔ x = 15$
3, $4x – 40 = |-4| + 12$
$⇔ 4x – 40 = 4 + 12$
$⇔ 4x - 40 = 16$
$⇔ 4x = 56$
$⇔ x = 56 : 4$
$⇔ x = 14$
4, $x + 15 = 20 – 4x$
$⇔ x + 4x = 20 - 15$
$⇔ 5x = 5$
$⇔ x = 5 : 5$
$⇔ x = 1$
5, $8x + |-3| = -4x + 39$
$⇔ 8x + 3 = -4x + 39$
$⇔ 8x + 4x = 39 - 3$
$⇔ 8x + 4x = 36$
$⇔ 12x = 36$
$⇔ x = 36 : 12$
$⇔ x = 3$
6, $6(x – 2) + (-2) = 20 – 4x$
$⇔6x - 12 + (-2) = 20 - 4x$
$⇔ 6x - 14 = 20 - 4x$
$⇔ 6x + 4x = 20 + 14$
$⇔ 10x = 34$
$⇔ x = 34 : 10$
$⇔ x = \frac {17}{5} = 3,4$
Bài 5:
a. $2(x – 5) – 3(x + 7) = 14$
$⇔ 2x - 10 - 3x - 21 = 14$
$⇔ -x - 31 = 14$
$⇔ x = -31 - 14$
$⇔ x = -45$
b. $5(x – 6) – 2(x + 3) = 12$
$⇔ 5x - 30 - 2x - 6 = 12$
$⇔ 3x - 36 = 12$
$⇔ 3x = 48$
$⇔ x = 48 : 3$
$⇔ x = 16$
c. $3(x – 4) – (8 – x) = 12$
$⇔ 3x - 12 - 8 + x = 12$
$⇔ 4x - 20 = 12$
$⇔ 4x = 32$
$⇔ x = 32 : 4$
$⇔ x = 8$
d. $-7(3x – 5) + 2(7x – 14) = 28$
$⇔ -21x + 35 + 14x - 28 = 28$
$⇔ -7x - 7 = 28$
$⇔ -7x = 21$
$⇔ x = 21 : (-7)$
$⇔ x = -3$
e. $5(3 – 2x) + 5(x – 4) = 6 – 4x$
$⇔ 15 - 10x + 5x - 20 = 6 - 4x$
$⇔ -x - 11 = 0$
$⇔ x = -11$
f. $-5(2 – x) + 4(x – 3) = 10x - 15$
$⇔ -10 + 5x + 4x -12 = 10x - 15$
$⇔ -x = 7$
$⇔ x = -7$
g. $2(4x – 8) – 7(3 + x) = |-4|(3 – 2)$
$⇔ 8x - 16 - 21 - 7x = 4.1$
$⇔ x = 4 + 21 + 16$
$⇔ x = 41$
h. $8(x - |-7|) – 6(x – 2) = |-8|.6 - 50$
$⇔ 8(x - 7) - 6x + 12 = 8.6 - 50$
$⇔ 8x - 56 - 6x + 12 = 48 - 50$
$⇔ 2x = -2 - 12 + 56$
$⇔ 2x = 46$
$⇔ x = 46 : 2$
$⇔ x = 23$
k. $-7(5 – x) – 2(x – 10) = 15$
$⇔ -35 + 7x - 2x + 20 = 15$
$⇔ 5x = 15 - 20 + 35$
$⇔ 5x = 30$
$⇔ x = 30 : 5$
$⇔ x = 6$
l. $4(x – 1) – 3(x – 2) = -|-5|$
$⇔ 4x - 4 - 3x + 6 = -5$
$⇔ x = -5 + 4 - 6$
$⇔ x = -7$
m. $-4(x + 1) + 89(x – 3) = 24$
$⇔ -4x - 4 + 89x - 276 = 24$
$⇔ 85x = 295$
$⇔ x = 295 : 85$
$⇔ x = \frac {259}{85} = \frac {59}{17} = 3,5$
n. $5(x – 30) – 2(x + 6) = 9$
$⇔ 5x - 150 - 2x - 12 = 9$
$⇔ 3x = 171$
$⇔ x = 171 : 3$
$⇔ x = 57$
o. $-3(x – 5) + 6(x + 2) = 9$
$⇔ -3x + 15 + 6x + 12 = 9$
$⇔ 3x = -18$
$⇔ x = -18 : 3$
$⇔ x = -6$
p. $7(x – 9) – 5(6 – x) = - 6 + 11x$
$⇔ 7x - 63 - 30 + 5x = -6 + 11x$
$⇔ 12x = 98$
$⇔ x = 98 : 12$
$⇔ x = \frac {49}{6} = 4,2$
q. $10(x – 7) – 8(x + 5) = 6.(-5) + 24$
$⇔ 10x - 70 - 8x - 40 = -30 + 24$
$⇔ 2x = 104$
$⇔ x = 104 : 2$
$⇔x = 52$
CHÚC EM HỌC TỐT. XIN HAY NHẤT.
