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câu 1 : tìm a biết
a + b _c = 18 với b = 10 ; c = - 9
\(\Rightarrow a+10+9=18\)
\(a=18-19=-1\)
2a _ 3b + c = 0 với b = -2 ; c= - 4
\(2a+6-4=0\)
\(2a+2=0\)
\(2a=-2\)
\(a=-1\)
3a _ b _ 2c = 2 với b = 6 ; c = - 1
\(3a-6+2=2\)
\(3a-8=2\)
\(3a=10\)
\(a=\frac{10}{3}\)
12 _ a + b + 5c = - 1 với b = - 7 ; c = 5
\(12-a-7+25=-1\)
\(12-a-7=-26\)
\(12-a=-19\)
\(a=31\)
1 _ 2b + c _ 3a = -9 với b = -3 ; c = 7
\(1+6+7-3a=-9\)
\(14-3a=9\)
\(3a=5\)
\(a=\frac{5}{3}\)
\(\left(2x-3\right)\left(6-2x\right)=0\)
\(\Leftrightarrow\orbr{\begin{cases}2x-3=0\\6-2x=0\end{cases}\Leftrightarrow\orbr{\begin{cases}x=\frac{3}{2}\\x=3\end{cases}}}\)
Vậy ...
\(2.\left|\frac{1}{2}x-\frac{1}{3}\right|-\frac{3}{2}=\frac{1}{4}\)
\(\Leftrightarrow2.\left|\frac{1}{2}x-\frac{1}{3}\right|=\frac{7}{4}\)
\(\Leftrightarrow\left|\frac{1}{2}x-\frac{1}{3}\right|=\frac{7}{8}\)
\(\Leftrightarrow\orbr{\begin{cases}\frac{1}{2}x-\frac{1}{3}=\frac{7}{8}\\\frac{1}{2}x-\frac{1}{3}=\frac{-7}{8}\end{cases}}\)
\(\Leftrightarrow\orbr{\begin{cases}x=\frac{29}{12}\\x=\frac{-13}{12}\end{cases}}\)
Vậy..
a=-3 -> a=3
a=0 -> a=0
a=7 -> a=7
a=-2 -> a=2
a=1 -> a=1
a=-9 -> a=9
a=4 ->a=4
4:
a: =4/15-2,9+11/15=1-2,9=-1,9
b: \(=-36,75+3,7-63,25+6,3=10-100=-90\)
c: \(=6,5+3,5-\dfrac{10}{17}-\dfrac{7}{17}=10-1=9\)
d: \(=\dfrac{13}{25}\left(-39,1-60,9\right)=\dfrac{13}{25}\left(-100\right)=-52\)
e: =-5/12-7/12-3,7-6,3=-1-10=-11
f: =2,8(-6/13-7/13)-7,2=-2,8-7,2=-10
`@` `\text {Ans}`
`\downarrow`
`1,`
`a)`
`-7/25 + (-8)/25`
`= (-7 - 8)/25`
`= -15/25`
`= -3/5`
`b)`
`6/13 + (-15)/39`
`= 18/39 + (-15)/39`
`= (18 - 15)/39`
`= 3/39`
`= 1/13`
`c)`
`5/7 + 4/(-14)`
`= 10/14 + (-4)/14`
`= (10 - 4)/14`
`= 6/14`
`= 3/7`
`d)`
`-8/18 + (-15)/27`
`= -4/9 + (-5)/9`
`= (-4-5)/9`
`= -9/9 = -1`
`2,`
`a)`
`3/5 + (-7)/4`
`= 12/20 + (-35)/20`
`= (12 - 35)/20`
`=-23/20`
`b)`
`(-2) + (-5)/8`
`= (-16)/8 + (-5)/8`
`= (-16 - 5)/8`
`= -21/8`
`c)`
`1/8 + (-5)/9`
`= 9/72 + (-40)/72`
`= (9-40)/72`
`= -31/72`
`d)`
`6/13 + (-14)/39`
`= 18/39 + (-14)/39`
`= (18 - 14)/39`
`= 4/39`
`e)`
`(-18)/24 + 15/21`
`= (-3)/4 + 5/7`
`= (-21)/28 + 20/28`
`= (-21 + 20)/28`
`= -1/28`
a, \(2^4:2^3+3\left|10\right|-\left(-18\right)\)
\(=2+3\cdot10+18\)
\(=20+30=50\)
b, \(\frac{1}{2}-\frac{1}{3}+9\left(-\frac{1}{2}\right)^2-\frac{1}{-6}\)
\(=\frac{1}{2}-\frac{1}{3}+9\cdot\frac{1}{4}+\frac{1}{6}\)
\(=\frac{3}{6}-\frac{2}{6}+\frac{9}{4}+\frac{1}{6}\)
\(=\frac{1}{6}+\frac{1}{6}+\frac{9}{4}=\frac{1}{3}+\frac{9}{4}=\frac{4}{12}+\frac{27}{12}=\frac{31}{12}\)