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Ta có :1.2+2.4+3.6+4.8+5.10/3.4+6.8+9.12+12.16+15.20=[1.2(1+4+9+...+25)]/[3.4(1+4+9+16)]
=(1.2)/(3.4)=2/12=1/6
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a)\(\dfrac{x}{60}=-\dfrac{3}{4}\)
\(\Rightarrow x\cdot4=60\cdot\left(-3\right)\)
\(x\cdot4=-180\)
x=45
b)\(\dfrac{2}{5}=\dfrac{12}{x}\)
\(\Rightarrow2x=5\cdot12\)
\(2x=60\)
x=30
c)\(x-\dfrac{5}{7}=\dfrac{6}{21}\)
\(x=\dfrac{2}{7}+\dfrac{5}{7}\)
x=1
d)\(x+\dfrac{7}{8}=\dfrac{63}{24}\)
\(x=\dfrac{21}{8}-\dfrac{7}{8}\)
\(\dfrac{14}{8}\)
a; \(\dfrac{x}{8}\) = \(\dfrac{3}{4}\) + \(\dfrac{-5}{8}\)
\(\dfrac{x}{8}\) = \(\dfrac{1}{8}\)
\(x\) = \(\dfrac{1}{8}\) \(\times\) 8
\(x\) = 1
b; \(\dfrac{x}{12}\) = \(\dfrac{3}{4}\) + \(\dfrac{-2}{3}\)
\(\dfrac{x}{12}\) = \(\dfrac{1}{12}\)
\(x\) = \(\dfrac{1}{12}\) \(\times\) 12
\(x\) = 1
c; 1 + \(\dfrac{11}{3}\) = \(\dfrac{24}{x}\)
\(\dfrac{14}{3}\) = \(\dfrac{24}{x}\)
\(x\) = 24 : \(\dfrac{14}{3}\)
\(x\) = \(\dfrac{36}{7}\)
d; \(\dfrac{x}{6}\) - \(\dfrac{3}{4}\) = \(\dfrac{1}{12}\)
\(\dfrac{x}{6}\) = \(\dfrac{1}{12}\) + \(\dfrac{3}{4}\)
\(\dfrac{x}{6}\) = \(\dfrac{5}{6}\)
\(x\) = \(\dfrac{5}{6}\) \(\times\) 6
\(x\) = 5
a: =7/8:(2/9-18+1/36)-5/12
=-7/142-5/12=-397/852
b: =3/7(4/9+5/9:6/12)=2/3
c: =5^8(16/31-47/31)+1/3=-5^8+1/3
d: =7/2(3/8+5/8:4/15)=609/64
`(x+2)-2=0`
`=>x+2=0+2`
`=>x+2=2`
`=>x=2-2`
`=>x=0`
__
`(x+3)+1=7`
`=>x+3=7-1`
`=>x+3=6`
`=>x=6-3`
`=>x=3`
__
`(x+3)+4=12`
`=>x+3=12-4`
`=>x+3=8`
`=>x=8-3`
`=>x=5`
__
`(5x+4)-1=13`
`=>5x+4=13+1`
`=>5x+4=14`
`=>5x=14-4`
`=>5x=10`
`=>x=10:5`
`=>x=2`
__
`(4x-8)+3=12`
`=>4x-8=12-3`
`=>4x-8=9`
`=>4x=9+8`
`=>4x=17`
`=> x=17/4`
__
`3+(x-5)=14`
`=>x-5=14-3`
`=>x-5=11`
`=>x=11+5`
`=>x=16`
1) |x + 2| = 4
\(\Leftrightarrow\orbr{\begin{cases}x+2=4\\x+2=-4\end{cases}\Leftrightarrow}\orbr{\begin{cases}x=2\\x=-6\end{cases}}\)
2) 3 – |2x + 1| = (-5)
\(\Leftrightarrow\left|2x+1\right|=8\Leftrightarrow\orbr{\begin{cases}2x+1=8\\2x+1=-8\end{cases}\Leftrightarrow}\orbr{\begin{cases}x=\frac{7}{2}\\x=\frac{-9}{2}\end{cases}}\)
3) 12 + |3 – x| = 9
\(\Leftrightarrow\left|3-x\right|=-3\)(vô lí)
=>\(x=\varnothing\)
1) I x+2 I=4
\(\Rightarrow\orbr{\begin{cases}x+2=4\\x+2=-4\end{cases}\Leftrightarrow\orbr{\begin{cases}x=2\\x=-6\end{cases}}}\)
2) \(3-|2x+1|=-5\)
\(\Leftrightarrow|2x+1|=8\)
\(\Leftrightarrow\orbr{\begin{cases}2x+1=8\\2x+1=-8\end{cases}\Leftrightarrow\orbr{\begin{cases}2x=7\\2x=-9\end{cases}\Leftrightarrow}\orbr{\begin{cases}x=\frac{7}{2}\\x=\frac{-9}{2}\end{cases}}}\)
3) \(12+|3-x|=9\)
\(\Leftrightarrow|3-x|=-3\)(vô lí vì I 3-x I \(\ge\)0)
`x/8 = 3/4 +(-5/8)`
`=>x/8 = 6/8 +(-5/8)`
`=>x/8 = 1/8`
`=>x=1`
`-----`
`x/12 =3/4 +(-2/3)`
`=>x/12 = 9/12 + (-8/12)`
`=> x/12=1/12`
`=>x=1`
`----`
`1+11/13=24/x`
`=> 13/13 +11/13=24/x`
`=> 24/13 =24/x`
`=>x=13`
`----`
`x/6 -3/4=1/12`
`=>x/6 = 1/12 +3/4`
`=>x/6 = 1/12 + 9/12`
`=>x/6 = 10/12`
`=>x/6= 5/6`
`=>x=5`
\(a,\Leftrightarrow\left[{}\begin{matrix}x-3=6\\x-3=-6\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=9\\x=-3\end{matrix}\right.\)
Vậy ...
\(b,\Leftrightarrow\left|x\right|=12-8=4\)
\(\Leftrightarrow x=\pm4\)
Vậy ...
c, Xem lại đề nha bạn .
d, Thấy : \(\left(\dfrac{3}{4}-x\right)^2\ge0\)
Vậy phương trình vô nghiệm
a) |x - 3| = 6
\(\Rightarrow\left[{}\begin{matrix}x-3=6\\x-3=-6\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=9\\x=-3\end{matrix}\right.\)
Vậy x = 9 hoặc x = - 3
b) 12 - |x| = 8
\(\Rightarrow\) |x| = 4
\(\Rightarrow\left[{}\begin{matrix}x=4\\x=-4\end{matrix}\right.\)
Vậy x = 4 hoặc x = - 4
\(3\left(x-4\right)-\left(8-x\right)=12\)
\(3x-12-8+x=12\)
\(4x=32\)
\(x=8\)
x=8 nha
hk tốt