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X - 6 : 2 - (48 - 24) : 2 : 6 - 3 = 0
X - 3 - 24 : 2 : 6 - 3 = 0
X - 3 - 2 - 3 = 0
X = 0 + 3 + 2 + 3
X = 8
X - 6 : 2 - ( 48 - 24 ) : 2 : 6 - 3 = 0
X - 6 : 2 - 24 : 2 : 6 - 3 = 0
X - 3 - 12 : 6 - 3 = 0
X - 3 - 2 - 3 = 0
X = 0 + 3 + 2 + 3
X = 8
( 3 x X - 16 ) x 6 = 2 x 42
( 3 x X - 16 ) x 6 = 84
3 x X - 16 = 14
3 x X = 30
X = 10
Vậy : X = 10
(3×x-16)×6=84
(3×x-16)=84:6
(3×x-16)=14
3x=14+16
3x=30
x=30:3
x=10
vậy x=10
a) \(\left(x-6\right)^2=9=3^2\)
\(\Rightarrow x-6=3\) hay \(x-6=-3\)
\(\Rightarrow x=9\) hay \(x=3\)
b) \(4^{2x-6}=1=4^0\)
\(\Rightarrow2x-6=0\Rightarrow x=3\)
a) \(\left(x-6\right)^2=9\)
\(\Rightarrow\left(x-6\right)^2=3^2\)
\(\Rightarrow\left[{}\begin{matrix}x-6=-3\\x-6=3\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}x=6\\x=9\end{matrix}\right.\)
b) \(4^{2x-6}=1\)
\(\Rightarrow4^{2x-6}=4^0\)
\(\Rightarrow2x-6=0\)
\(\Rightarrow2x=6\)
\(\Rightarrow x=3\)
\(1+\dfrac{1}{3}+\dfrac{1}{6}+\dfrac{1}{10}+...+\dfrac{2}{x\left(x+1\right)}=1\dfrac{1989}{1991}\)
\(\Rightarrow2\left(\dfrac{1}{2}+\dfrac{1}{6}+\dfrac{1}{12}+\dfrac{1}{20}+...+\dfrac{1}{x\left(x+1\right)}\right)=\dfrac{3980}{1991}\)
\(\Rightarrow2\left(\dfrac{1}{1.2}+\dfrac{1}{2.3}+\dfrac{1}{3.4}+\dfrac{1}{4.5}+...+\dfrac{1}{x\left(x+1\right)}\right)=\dfrac{3980}{1991}\)
\(\Rightarrow2\left(1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{5}+...+\dfrac{1}{x}-\dfrac{1}{x+1}\right)=\dfrac{3980}{1991}\)
\(\Rightarrow2\left(1-\dfrac{1}{x+1}\right)=\dfrac{3980}{1991}\)
\(\Rightarrow1-\dfrac{1}{x+1}=\dfrac{3980}{1991}.\dfrac{1}{2}\)
\(\Rightarrow1-\dfrac{1}{x+1}=\dfrac{1990}{1991}\)
\(\Rightarrow\dfrac{1}{x+1}=1-\dfrac{1990}{1991}\)
\(\Rightarrow\dfrac{1}{x+1}=\dfrac{1}{1991}\)
\(\Rightarrow x+1=1991\)
\(\Rightarrow x=1990\)