Question

Bài 3 (2đ): Tìm x biết:

a. (x - 8 )( x³+ 8) = 0

b. (4x - 3) – ( x + 5) = 3(10 - x)

Answer 1

\(a.\)

\(\left(x-8\right)\left(x^3+8\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x-8=0\\x^3+8=0\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x=8\\x^3=-8\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x=8\\x=-2\end{matrix}\right.\)

\(S=\left\{8,-2\right\}\)

\(b.\)

\(\left(4x-3\right)-\left(x+5\right)=3\cdot\left(10-x\right)\)

\(\Leftrightarrow4x-3-x-5-30+3x=0\)

\(\Leftrightarrow6x-38=0\)

\(\Leftrightarrow x=\dfrac{38}{6}\)

\(S=\left\{\dfrac{38}{6}\right\}\)

Answer 2

a) \(\left(x-8\right)\left(x^3+8\right)=0\)

=>\(x-8=0 => x=8\)

hoặc \(x^3+8=0\)=>\(x=-2\)

b) \(\left(4x-3\right)-\left(x+5\right)=3\left(10-x\right)\)

\(< =>3x-8=3\left(10-x\right)\)

\(< =>3x-8-30+3x=0\)

\(< =>6x=38=>x=\dfrac{38}{6}=\dfrac{19}{3}\)