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câu 1 :
\(A=\frac{-7}{12}:\frac{49}{11}\cdot\frac{5}{121}-\frac{7}{6}\) \(B=\frac{1}{8}-\frac{8}{7}:8-3:\frac{3}{4}\cdot-2^3\)
\(A=\frac{-11}{84}\cdot\frac{5}{121}-\frac{7}{6}\) \(B=\frac{1}{8}-\frac{8}{7}:\frac{8}{1}-\frac{3}{1}:\frac{3}{4}\cdot\left(-2^3\right)\)
\(A=\frac{-5}{924}-\frac{7}{6}\) \(B=\frac{1}{8}-\frac{1}{7}-\left(-32\right)\)
\(A=\frac{-361}{308}\) \(B=\frac{-1}{56}-\left(-32\right)\)
\(B=\frac{1791}{56}\)
Câu 2 :
a)\(\frac{22}{7}:x=\frac{11}{7}\) b)\(\left(1-3x\right)\cdot\frac{4}{3}=-2^3\)
\(x=\frac{22}{7}:\frac{11}{7}\) \(\left(1-3x\right)\cdot\frac{4}{3}=-8\)
\(x=2\) \(\left(1-3x\right)=-8:\frac{4}{3}\)
\(\left(1-3x\right)=-6\)
\(3x=-6-1=7\)
\(3x=7:3=\frac{7}{3}\)
c ) bằng \(\frac{27}{5}\)nhé
\(C=\frac{3}{3.5}+\frac{3}{5.7}+......+\frac{3}{47.49}\)
\(=\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+.....+\frac{1}{47}-\frac{1}{49}\)
\(=\frac{1}{3}-\frac{1}{49}\)
a)
C = \(\frac{3}{3.5}+\frac{3}{5.7}+\frac{3}{7.9}+........+\frac{3}{47.49}\)
C = \(\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+\frac{1}{9}-.........-\frac{1}{47}+\frac{1}{47}-\frac{1}{49}\)
C = \(\frac{1}{3}-\frac{1}{49}\)
C = \(\frac{49}{147}-\frac{3}{147}\)
C = \(\frac{46}{147}\)
b) \(\frac{7}{2}.\left(\frac{1}{2}-x\right)-\frac{1}{8}=\frac{3}{4}\)
\(\frac{7}{2}.\left(\frac{1}{2}-x\right)=\frac{3}{4}+\frac{1}{8}\)
\(\frac{7}{2}.\left(\frac{1}{2}-x\right)=\frac{24}{32}+\frac{4}{32}\)
\(\frac{7}{2}.\left(\frac{1}{2}-x\right)=\frac{28}{32}\)
\(\frac{1}{2}-x=\frac{28}{32}:\frac{7}{2}\)
\(\frac{1}{2}-x=\frac{7}{8}.\frac{2}{7}\)
\(\frac{1}{2}-x=\frac{1}{4}\)
\(x=\frac{1}{2}-\frac{1}{4}\)
\(x=\frac{2}{4}-\frac{1}{4}=\frac{1}{4}\)
Vậy x = \(\frac{1}{4}\)
bài 3:
a, đặt \(\dfrac{x}{12}=\dfrac{y}{9}=\dfrac{z}{5}=k\)
=>x=12k,y=9k,z=5k
ta có: ayz=20=> 12k.9k.5k=20
=> (12.9.5)k^3=20
=>540.k^3=20
=>k^3=20/540=1/27
=>k=1/3
=>x=12.1/3=4
y=9.1/3=3
z=5.1/3=5/3
vậy x=4,y=3,z=5/3
b,ta có: \(\dfrac{x}{5}=\dfrac{y}{7}=\dfrac{z}{3}=\dfrac{x^2}{25}=\dfrac{y^2}{49}=\dfrac{z^2}{9}\)
A/D tính chất dãy tỉ số bằng nhau ta có:
\(\dfrac{x}{5}=\dfrac{y}{7}=\dfrac{z}{3}=\dfrac{x^2}{25}=\dfrac{y^2}{49}=\dfrac{z^2}{9}=\dfrac{x^2+y^2-z^2}{25+49-9}=\dfrac{585}{65}=9\)
=>x=5.9=45
y=7.9=63
z=3*9=27
vậy x=45,y=63,z=27
a: =>5x=3x-6
=>2x=-6
hay x=-3
b: \(\Leftrightarrow\left(x-3\right)^2=4\cdot5^2=100\)
=>x-3=10 hoặc x-3=-10
=>x=13 hoặc x=-7
c: \(\left|x^3+1\right|+2\ge2\forall x\)
Dấu '=' xảy ra khi x=-1
a)
(x+2)2+(y-3)2+(z-2)2=0
\(\Rightarrow\hept{\begin{cases}\left(x+2\right)^2=0\\\left(y-3\right)^2=0\\\left(z-2\right)^2=0\end{cases}\Rightarrow\hept{\begin{cases}x=-2\\y=3\\z=2\end{cases}}}\)
Vậy...
b)
(x-3).y-x=5
xy - 3x - x = 5
xy - 4x = 5
x(y - 4) = 5 = 1.5 = (-1).(-5)
TH1:
\(\Rightarrow\hept{\begin{cases}x=1\\y-4=5\end{cases}\Rightarrow\hept{\begin{cases}x=1\\y=9\end{cases}}}\)
TH2:
\(\Rightarrow\hept{\begin{cases}x=5\\y-4=1\end{cases}\Rightarrow\hept{\begin{cases}x=5\\y=5\end{cases}}}\)
TH3:
\(\Rightarrow\hept{\begin{cases}x=-1\\y-4=-5\end{cases}\Rightarrow\hept{\begin{cases}x=-1\\y=-1\end{cases}}}\)
TH4:
\(\Rightarrow\hept{\begin{cases}x=-5\\y-4=-1\end{cases}\Rightarrow\hept{\begin{cases}x=-5\\y=3\end{cases}}}\)
Vậy...
a ) 9x - 49 = 104
9x = 104 + 49
9x = 153
x = 153 : 9
x = 17
b) 80 - 7 ( x - 3 ) = 45
7 ( x - 3 ) = 80 - 45
7 ( x - 3 ) = 35
x - 3 = 35 : 7
x - 3 = 5
x = 5 + 3
x = 8
c ) 3 x + 2 - 43 = 38
3 x + 2 = 38 + 43
3 x + 2 = 81
3 x + 2 = 3 4
=> x + 2 = 4
x = 4 - 2
x = 2