Question

[Kim Seok Jin]

tìm x thuộc Z biết

a, (/x/ +3 ):5-3 =12

b, 86 : [2.(2x - 1 )² - 7] +4² = 2.3²

Answer 1

[Cold Wind]

a) \(\left(\left|x\right|+3\right):5-3=12\Leftrightarrow\left|x\right|+3=45\Leftrightarrow\orbr{\begin{cases}x=42\\x=-42\end{cases}}\)

b) \(86:\left[2\left(2x-1\right)^2-7\right]+4^2=2\cdot3^2\Leftrightarrow2\left(2x-1\right)^2-7=43\Leftrightarrow\left(2x-1\right)^2=25\Leftrightarrow\orbr{\begin{cases}2x-1=-5\\2x-1=5\end{cases}\Leftrightarrow}\orbr{\begin{cases}x=-2\\x=3\end{cases}}\)

Answer 2

[Trần Thảo Vân]

a) \(\left(\left|x\right|+3\right)\div5-3=12\)

    \(\left(\left|x\right|+3\right)\div5=12+3\)

    \(\left(\left|x\right|+3\right)\div5=15\)

       \(\left|x\right|+3=15.5\)

       \(\left|x\right|+3=75\)

       \(\left|x\right|=75-3\)

       \(\left|x\right|=72\)

\(\Rightarrow\orbr{\begin{cases}x=72\\x=-72\end{cases}}\)

Vậy \(x\in\left\{72;-72\right\}\)

b) \(86\div\left[2,\left(2x-1\right)^2-7\right]+4^2=2.3^2\)

    \(86\div\left[2.\left(2x-1\right)^2-7\right]+16=18\)

    \(86\div\left[2.\left(2x-1\right)^2-7\right]=18-16\)

    \(86\div\left[2.\left(2x-1\right)^2-7\right]=2\)

                  \(2.\left(2x-1\right)^2-7=86\div2\)

                  \(2.\left(2x-1\right)^2-7=43\)

                  \(2.\left(2x-1\right)^2=43+7\)

                  \(2.\left(2x-1\right)^2=50\)

                      \(\left(2x-1\right)^2=50\div2\)

                      \(\left(2x-1\right)^2=25\)    

                      \(\left(2x-1\right)^2=5^2\)

\(\Rightarrow2x-1=5\)

                \(2x=5+1\)

                \(2x=6\)

                  \(x=6\div2\)

                  \(x=3\)