2 PHẦN 7 CUA 491 LÀ bao nhiêu

(4x - 3) - (x + 5) = 3(10-x)

4x - 3 - x - 5       = 30 - 3x

(4x - x) - (3+5)   = 30 - 3x

3x    - 8              = 30 - 3x

3x + 3x               = 30 + 8

6x                        = 38

    x             = 38 : 6

   x           = 19/3

Vậy x    = 19/3

mình ko bt có đúng ko

\(\frac{a+3}{5}=\frac{b-2}{3}=\frac{c-1}{7}\)

=> \(\frac{3a+9}{15}=\frac{5b-10}{15}=\frac{7c-7}{49}=\frac{3a+9-5b+10+7c-7}{15-15+49}\)

                                                                    \(=\frac{3a-5b+7c+12}{49}=\frac{86+12}{49}=\frac{98}{49}=2\)

=> \(\hept{\begin{cases}\frac{a+3}{5}=2\\\frac{b-2}{3}=2\\\frac{c-1}{7}=2\end{cases}}\Leftrightarrow\hept{\begin{cases}a+3=10\\b-2=6\\c-1=14\end{cases}}\Leftrightarrow\hept{\begin{cases}a=7\\b=8\\c=15\end{cases}}\)

\(x^3-8+2x\left(x-2\right)=\left(x-2\right)\left(x^2+2x+4\right)+2x\left(x-2\right)\)

\(=\left(x-2\right)\left(x^2+4x+4\right)=\left(x-2\right)\left(x+2\right)\left(x+2\right)\)

\(\frac{16}{81}=\left(\frac{4}{9}\right)^2=\left(-\frac{4}{9}\right)^2=\left(\frac{2}{3}\right)^2=\left(-\frac{2}{3}\right)^2\)

lộn rồi

\(\frac{16}{81}=\left(\frac{4}{9}\right)^2=\left(-\frac{4}{9}\right)^2=\left(\frac{2}{3}\right)^4=\left(-\frac{2}{3}\right)^4\)

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