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a, Xét : \(\frac{x}{-30}=-\frac{12}{20}=-\frac{3}{5}\Leftrightarrow5x=90\Leftrightarrow x=18\)
Xét : \(\frac{-36}{y}=\frac{-3}{5}\Leftrightarrow3y=180\Leftrightarrow y=60\)
Vậy \(x=18;y=60\)
b, \(\frac{x-1}{7}=\frac{2y+5}{3}\)và \(x+2y=-16\)
Áp dụng tính chất dãy tỉ số bằng nhau ta có :
\(\frac{x-1}{7}=\frac{2y+5}{3}=\frac{x+2y-1+5}{7+3}=\frac{-16+4}{10}=\frac{-12}{10}=-\frac{6}{5}\)
\(\Leftrightarrow\frac{x-1}{7}=-\frac{6}{5}\Leftrightarrow5x-5=-42\Leftrightarrow5x=-37\Leftrightarrow x=-\frac{37}{5}\)
\(\Leftrightarrow\frac{2y+5}{3}=-\frac{6}{5}\Leftrightarrow10y+25=-18\Leftrightarrow10y=-43\Leftrightarrow y=-\frac{43}{10}\)
1. -x+20 = -(-15)-8+13
=> -x=15-8+13-20
=> -x=0
=> x=0
2. -(-10)+x=-13+(-9)+(-6)
=> 10+x=-13-9-6
=> x = -13-9-6-10
=> x = -38
3. 8-(-12)+10=-(-14)-x
=> 8+12+10=14-x
=> x = 14-8-12-10
=> x = -16
4. -(+12)+(-x)-(-3)=5-(-7)
=> -12-x+3=5+7
=> -x=5+7+12-3
=> -x=21
=> x=-21
5. 14-x+(-10)=-(-9)+(+15)
=> 14-x-10=9+15
=> -x=9+15-14+10
=> -x=20
=> x=-20
6. 12-(-17)+(-3)=-5+x
=> 12+17-3+5=x
=> x=31
7. x-(-19)-(+32)=14-(+16)
=> x+19-32=14-16
=> x=14-16+32-19
=> x=11
8. x-|-15|-|7|=-(-9)+|-5|
=> x-15-7=9+5
=> x=9+5+7+15
=> x=36
9. 15-x+17=13-(-21)
=> 15-x+17=13+21
=> -x=13+21-15-17
=> -x=2
=> x=-2
10. -|-5|-(-x)+4=3-(-25)
=> -5+x+4=3+25
=> x=3+25-4+5
=> x=29
Bài 1:
a,x=11
b,không tồn tại giá trị của x
c,x=-3
Bài 2:
a,=300
b,=51
-x + 20 = - (-15) - (8) + 13
-x + 20 = 15 - 8 + 13
-x + 20 = 7 + 13
- x + 20 = 20
x = 20 - 20
x = 0
-(-10) + x = -13 + (-9) + (-6)
10 + x = -13 - 9 - 6
10 + x = -28
x = -28 - 10
x = -38
a) \(\left(x-7\right)-\left(5-x\right)=12-\left(-8+x\right)\)
\(\Leftrightarrow x-7-5+x=12+8-x\)
\(\Leftrightarrow2x-12=20-x\)
\(\Leftrightarrow2x+x=12+20\)
\(\Leftrightarrow3x=32\)
\(\Leftrightarrow x=\frac{32}{3}\)
b) 124 + ( 13 - 16 ) = 162 - ( x + 162 )
<=> 124 - 3 = 162 - x - 162
<=> 121 = -x
<=> x = -121
a) -12.(x - 5) + 7(3 - x) = 5
=> -12x + 60 + 21 - 7x = 5
=> -19x + 81 = 5
=> -19x = 5 - 81
=> -19x = -76
=> x = -76 : (-19)
=> x = 4
b) (x + 1) + (x + 2) + (x + 3) + ... + (x + 20) = 250
=> (x + x + x + ... + x) + (1 + 2 + 3 + ... + 20) = 250
=> 20x + 210 = 250
=> 20x = 250 - 210
=> 20x = 40
= > x = 40 : 20
=> x = 2
\(-12\left(x-5\right)+7\left(3-x\right)=5\)
\(\Leftrightarrow-12x+60+21-7x=5\)
\(\Leftrightarrow-19x+81=5\)
\(\Leftrightarrow81-5=19x\)
\(\Leftrightarrow19x=76\)
\(\Leftrightarrow x=4\)
a) \(\dfrac{13}{20}+\dfrac{3}{5}+x=\dfrac{5}{6}\)
\(\Rightarrow\dfrac{5}{4}+x=\dfrac{5}{6}\)
\(\Rightarrow x=\dfrac{5}{6}-\dfrac{5}{4}\)
\(\Rightarrow x=\dfrac{-5}{12}\)
b) \(x+\dfrac{1}{3}=\dfrac{2}{5}-\dfrac{-1}{3}\)
\(\Rightarrow x+\dfrac{1}{3}=\dfrac{11}{15}\)
\(\Rightarrow x=\dfrac{11}{15}-\dfrac{1}{3}\)
\(\Rightarrow x=\dfrac{2}{5}\)
c)\(\dfrac{-5}{8}-x=\dfrac{-3}{20}-\dfrac{-1}{6}\)
\(\dfrac{-5}{8}-x=\dfrac{1}{60}\)
\(\Rightarrow x=\dfrac{-5}{8}-\dfrac{1}{60}\)
\(\Rightarrow x=\dfrac{-77}{120}\)
d) \(\dfrac{3}{5}-x=\dfrac{1}{4}+\dfrac{7}{10}\)
\(\Rightarrow\dfrac{3}{5}-x=\dfrac{19}{20}\)
\(\Rightarrow x=\dfrac{3}{5}-\dfrac{19}{20}\)
\(\Rightarrow x=\dfrac{-7}{20}\)
e) \(\dfrac{-3}{7}-x=\dfrac{4}{5}+\dfrac{-2}{3}\)
\(\Rightarrow\dfrac{-3}{7}-x=\dfrac{2}{15}\)
\(\Rightarrow x=\dfrac{-3}{7}-\dfrac{2}{15}\)
\(\Rightarrow x=\dfrac{-59}{105}\)
g) \(\dfrac{-5}{6}-x=\dfrac{7}{12}+\dfrac{-1}{3}\)
\(\Rightarrow\dfrac{-5}{6}-x=\dfrac{1}{4}\)
\(\Rightarrow x=\dfrac{-5}{6}-\dfrac{1}{4}\)
\(\Rightarrow x=\dfrac{-13}{12}\)
a) x+5=20-(12-7)
x+5=15
x =10
b) 12-3.(x+2)=3
3.(x+2)=9
x+2 =3
x =1
c) |x-3|-16=-4
|x-3| =-4+16
|x-3| =12
=> x-3=12 (1)
hoặc x-3=-12 (2)
Từ (1), => x=15
Từ (2) => x=-9
Vậy x={-9;15}
a, x + 5= 20-(12-7)
x = -5+ 20- 5 = 10
x= 10
b, 12-3.(x+2)=3
-3.(x+2)= 3-12
-3x- 6 = -9
3x= 3
x= 1
c, | x-3|-16= -4
|x-3|= 16-4
|x-3|= 12
Trường hợp 1:
x-3= 12
x= 15
Trường hợp 2:
-(x-3)=12
-x+3= 12
x= -9