Question

(3x + 21)^{3= \(\dfrac{27}{8}\)}

Answer 1

(3x+21)³=\(\dfrac{27}{8}\)

\(\Rightarrow\)(3x+21)³=\(\left(\dfrac{3}{2}\right)^3\)

\(\Rightarrow\)3x+21=\(\dfrac{3}{2}\)

\(\Rightarrow\)3x =\(\dfrac{3}{2}\)-21=\(\dfrac{-39}{2}\)

\(\Rightarrow\)x =\(\dfrac{-39}{2}\):3

\(\Rightarrow\) =\(\dfrac{-13}{2}\)

Vậy x =\(\dfrac{-13}{2}\)

Answer 2

\(\left(3x+21\right)^3=\dfrac{27}{8}\)

\(\Rightarrow3x+3.7=\dfrac{1}{2}.3\)

\(\Rightarrow x+7=\dfrac{1}{2}\)

\(\Rightarrow x=-7\dfrac{1}{2}\)

Answer 3

Giải:

\(\left(3x+21\right)^3=\dfrac{27}{8}\)

\(\Leftrightarrow\left(3x+21\right)^3=\left(\dfrac{3}{2}\right)^3\)

Vì \(3=3\)

Nên \(3x+21=\dfrac{3}{2}\)

\(\Leftrightarrow3x=\dfrac{3}{2}-21\)

\(\Leftrightarrow3x=-\dfrac{39}{2}\)

\(\Leftrightarrow x=-\dfrac{39}{2}:3\)

\(\Leftrightarrow x=-\dfrac{13}{2}\)

Vậy \(x=-\dfrac{13}{2}\).