\(\left(x+15\right):3=7\)

\(x+15=7.3\)

\(x+15=21\)

\(x=21-15\)

\(x=6\)

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\(4.\left(6-x\right)=280:36\)

\(4.\left(6-x\right)=\dfrac{70}{9}\)

\(6-x=\dfrac{70}{9}:4\)

\(6-x=\dfrac{35}{18}\)

\(x=6-\dfrac{35}{18}\)

\(x=\dfrac{73}{18}\)

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\(5x-3x-12=8\)

\(2x=8+12\)

\(2x=20\)

\(x=\dfrac{20}{2}\)

\(x=10\)

\(\left(x+15\right):3=7\\ \Rightarrow x+15=7.3=21\\ \Rightarrow x=21-15=6\)

\(4\left(6-x\right)=280:36\\ \Rightarrow4\left(6-x\right)=\dfrac{70}{9}\\ \Rightarrow6-x=\dfrac{70}{9}:4\\ \Rightarrow6-x=\dfrac{35}{18}\\ \Rightarrow x=6-\dfrac{35}{18}=\dfrac{73}{18}\)

\(5x-3x-12=8\\ \Rightarrow2x=8+12=20\\ \Rightarrow x=\dfrac{20}{2}=10\)

=>1/10x=3/2

=>x=3/2*10=30/2=15

\(\dfrac{3}{5}x-\dfrac{1}{2}x=\dfrac{3}{2}-0\)

\(\left(\dfrac{3}{5}-\dfrac{1}{2}\right)x=\dfrac{3}{2}\)

\(\dfrac{1}{10}\cdot x=\dfrac{3}{2}\)

\(x=\dfrac{3}{2}:\dfrac{1}{10}\)

\(x=15\)

\(\dfrac{3}{5x}-\dfrac{1}{2x}=\dfrac{3}{2-0}\)

\(\dfrac{3}{5x}+\dfrac{-1}{2x}=\dfrac{3}{2}\)

\(\dfrac{3}{5}+\dfrac{-1}{2}=\dfrac{3}{2}\cdot x\)

\(\dfrac{1}{10}=\dfrac{3}{2}\cdot x\)

\(\dfrac{3}{2}\cdot x=\dfrac{1}{10}\)

     \(x=\dfrac{1}{10}\div\dfrac{3}{2}\)

    \(x=\dfrac{2}{30}\)

    \(x=\dfrac{1}{15}\)

3\(x^2\).(5\(x\) + 1) + 6\(x^3\).(5\(x\) + 2) = 9\(x^3\) .(5\(x\) + 3)

15\(x^3\) + 3\(x^2\) + 30\(x^4\) + 12\(x^3\) = 45\(x^4\) + 27\(x^3\)

(15\(x^3\) + 12\(x^3\)) + 3\(x^2\) + 30\(x^4\) - 45\(x^4\) - 27\(x^3\) = 0

       27\(x^3\) + 3\(x^2\)  - 15\(x^4\) - 27\(x^3\) = 0

                     3\(x^2\) - 15\(x^4\)      = 0

                     3\(x^2\).(1 - 5\(x^2\)) = 0

                         \(\left[{}\begin{matrix}x^2=0\\1-5x^2=0\end{matrix}\right.\)

                         \(\left[{}\begin{matrix}x=0\\5x^2=1\end{matrix}\right.\)

                          \(\left[{}\begin{matrix}x=0\\x=\mp\dfrac{\sqrt{5}}{5}\end{matrix}\right.\)  

d: \(\Leftrightarrow x+5=5\)

hay x=0

KHO THE

\(A=\frac{\left[\left(25-1\right):1+1\right]\left(25+1\right)}{2}=325.\)

\(B=\frac{\left[\left(51-3\right):2+1\right]\left(51+3\right)}{2}=675\)

\(C=\frac{\left[\left(81-1\right):4+1\right]\left(81+1\right)}{2}=861\)

Thiếu điều kiện về $x,y$ rồi bạn. Bạn bổ sung để được hỗ trợ tốt hơn.

Bài 3: 

1: =>2x=-5/3-1/2=-10/6-3/6=-13/6

hay x=-13/12

2: =>3/5x=1/7+3/5=5/35+21/35=26/35

hay x=26/3

3: =>-3x=5/6+3/4=10/12+9/12=19/12

hay x=-19/36

4: =>1/2x=3/7-5/4=12/28-35/28=-23/28

hay x=-23/14

5: =>1/4x=-3/5-7/5=-2

hay x=-8

6: =>3x=1/42+1/7=1/42+6/42=1/7

hay x=1/21

bạn có chắc đúng ko ạ

= -4800

=-4800