tìm x, biết
a, (2,8x - 32) : \(\frac{2}{3}\)= -90
b, \(\frac{4}{5}\)+\(\frac{5}{7}\): x = \(\frac{1}{6}\)
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a) \(\frac{-5}{8}\cdot\left(\frac{4}{9}+\frac{-7}{12}\right)\)
\(=\frac{-5}{8}\cdot\frac{-5}{36}\)
\(=\frac{25}{288}\)
b) \(\left(-3,2\right)\cdot\frac{-15}{64}+\left(0,8-2\frac{4}{5}\right):3\frac{1}{2}\)
\(=\frac{3}{4}+\left(-2\right):\frac{7}{2}\)
\(=\frac{3}{4}+\frac{-4}{7}\)
\(=\frac{5}{28}\)
=))
\(\frac{1}{2.5}+\frac{1}{5.8}+...+\frac{1}{\left(3n-1\right)\left(3n+2\right)}\)
\(=\frac{1}{3}.\left(\frac{3}{2.5}+\frac{3}{5.8}+...+\frac{3}{\left(3n-1\right)\left(3n+2\right)}\right)\)
\(=\frac{1}{3}.\left(\frac{1}{2}-\frac{1}{5}+\frac{1}{5}-\frac{1}{8}+...+\frac{1}{3n-1}-\frac{1}{3n+2}\right)\)
\(=\frac{1}{3}.\left(\frac{1}{2}-\frac{1}{3n+2}\right)\)
\(=\frac{1}{3}.\frac{3n}{2.\left(3n+2\right)}\)
\(=\frac{n}{2\left(3n+2\right)}\)
1) 274 x 8110
= (33)4 x (34)10
= 33 x 4 x 34 x 10
= 312 x 340
= 352
2) a) n16 = n3
=> n16 - n3 = 0
=> n3 x (n13 - 1) = 0
=> \(\orbr{\begin{cases}n^3=0\\n^{13}-1=0\end{cases}\Rightarrow\orbr{\begin{cases}n^3=0^3\\n^{13}=1^3\end{cases}\Rightarrow}\orbr{\begin{cases}n=0\\n=1\end{cases}}}\)
Vậy n = 0 hoặc n = 1
\(\left(2x-3\right)^{10x}=\left(3-2x\right)^{100}\)
\(\Leftrightarrow\left(2x-3\right)^{10x}=\left(2x-3\right)^{100}\)
\(\Leftrightarrow10x=100\Leftrightarrow x=100:10=10\)
Theo bài ra ta có : \(\frac{23+n}{40+n}=\frac{3}{4}\)
\(\Rightarrow4.\left(23+n\right)=3.\left(40+n\right)\)
\(\Rightarrow92+4n=120+3n\)
\(\Rightarrow4n-3n=120-92\)
\(\Rightarrow n=28\)
Vậy số n cần tìm là 28
(x + 3)(x2 - 36) = 0
<=> \(\orbr{\begin{cases}x+3=0\\x^2-36=0\end{cases}}\)<=> \(\orbr{\begin{cases}x=-3\\x=\pm6\end{cases}}\)
=> \(\orbr{\begin{cases}x=-3\\x=\pm6\end{cases}}\)
(x + 3) . (x^2 - 36) = 0
=> TH1: x + 3 = 0
x = -3
TH2: x^2 - 36 = 0
x^2 = 36
x^2 = 6^2
=> x = 6
Vậy x \(\in\){6 ; -3}
a ) (2,8x - 32 ) : 2/3 = -90
<=> 2,8x -32 = -60
<=> 2,8x = -28
<=> x = -10
b ) 4/5 + 5/7 :x =1/6
<=> 5/7:x = -19/30
<=> x = -150/133
a)\(\left(2,8x-32\right):\frac{2}{3}=-90\)
\(2,8x-32=-90\cdot\frac{2}{3}\)
\(2,8x-32=-60\)
\(2,8x=-60+32\)
\(2,8x=-28\)
\(x=-28:2,8\)
\(x=-10\)
Vậy x = -10
b) \(\frac{4}{5}+\frac{5}{7}:x=\frac{1}{6}\)
\(\frac{5}{7}:x=\frac{1}{6}-\frac{4}{5}\)
\(\frac{5}{7}:x=\frac{-19}{30}\)
\(x=\frac{5}{7}:\frac{-19}{30}\)
\(x=\frac{-150}{133}\)
Vậy x = -150/133
=))