7) ( 2x²+ 1)³= 729

=> ( 2x²+ 1)³ = 3⁶

=> ( 2x²+ 1)³= 9³

=> 2x²+ 1= 9

=> 2x²= 8

=> x²= 4

=> x= 2

8) ( 3x²- 43)³= 125

=> (3x²- 43)³= 5³

=> 3x²- 43= 5

=> 3x²= 48

=> x²= 16

=> x= 4

Vậy x=4

a, \(3x\left(\frac{1}{2.5}+\frac{1}{5.8}+\frac{1}{8.11}+\frac{1}{11.14}\right)=\frac{1}{21}\)

\(3x.\frac{1}{3}\left(\frac{1}{2}-\frac{1}{5}+\frac{1}{5}-...+\frac{1}{11}-\frac{1}{14}\right)=\frac{1}{21}\)

\(x.\left(\frac{1}{2}-\frac{1}{14}\right)=\frac{1}{21}\)

\(\frac{3x}{7}=\frac{1}{21}\Rightarrow x=\frac{1}{9}\)

Quên mất câu b.

Gọi số kg của quả dưa là x

=>\(\frac{3}{4}x=3\frac{1}{2}\Rightarrow\frac{3}{4}x=\frac{7}{2}\Rightarrow x=\frac{14}{3}=4\frac{2}{3}kg\)

Vậy....

a, dễ, tự làm

b, \(\dfrac{3x}{2.5}+\dfrac{3x}{5.8}+.........+\dfrac{3x}{11.14}=\dfrac{1}{21}\)

\(\Leftrightarrow x\left(\dfrac{3}{2.5}+\dfrac{3}{5.8}+.........+\dfrac{3}{11.14}\right)=\dfrac{1}{21}\)

\(\Leftrightarrow x\left(\dfrac{1}{2}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{8}+.....+\dfrac{1}{11}-\dfrac{1}{14}\right)=\dfrac{1}{21}\)

\(\Leftrightarrow x\left(\dfrac{1}{2}-\dfrac{1}{14}\right)=\dfrac{1}{21}\)

\(\Leftrightarrow x.\dfrac{3}{7}=\dfrac{1}{21}\)

\(\Leftrightarrow x=\dfrac{1}{9}\)

Vậy ...

a) (x-2)³ = (x-2)²

<=> (x-2)³-(x-2)² = 0

<=> (x-2)²(x-2-1) = 0

<=> \(\left\{{}\begin{matrix}\left(x-2\right)^2=0\\x-3=0\end{matrix}\right.\)

<=> \(\left\{{}\begin{matrix}x=2\\x=3\end{matrix}\right.\)

b) \(\dfrac{3x}{2.5}+\dfrac{3x}{5.8}+...+\dfrac{3x}{11.14}=\dfrac{1}{21}\)

<=> \(x\left(\dfrac{3}{2.5}+\dfrac{3}{5.8}+...+\dfrac{3}{11.14}\right)=\dfrac{1}{21}\)

<=> \(x\left(\dfrac{1}{2}-\dfrac{1}{14}\right)=\dfrac{1}{21}\)

<=> \(x=\dfrac{1}{21}:\dfrac{3}{7}\)

<=> \(x=\dfrac{1}{9}\)

1)-2x – (x – 17) = 34 – (-x + 25)

-2x-x-_17

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