Question

Đã trả lời bởi chuyên gia

Answer 1

\[\begin{array}{l}
\;a){\rm{ }}{x^3} - {\rm{ }}9x = 0.\\
\Leftrightarrow x\left( {{x^2} - 9} \right) = 0\\
\Leftrightarrow x\left( {x - 3} \right)\left( {x + 3} \right) = 0\\
\Leftrightarrow \left[ \begin{array}{l}
x = 0\\
x - 3 = 0\\
x + 3 = 0
\end{array} \right.\\
\Leftrightarrow \left[ \begin{array}{l}
x = 0\\
x = 3\\
x = - 3
\end{array} \right.\\
vay:S = \{ 0; - 3;3\} \\
b){\rm{ }}4{x^2} - 25 - \left( {2x - 5} \right)\left( {2x + 7} \right) = 0\\
\Leftrightarrow \left( {4{{\rm{x}}^2} - 25} \right) - \left( {2{\rm{x}} - 5} \right)\left( {2{\rm{x}} + 7} \right) = 0\\
\Leftrightarrow \left( {2{\rm{x}} - 5} \right)\left( {2{\rm{x}} + 5} \right) - \left( {2{\rm{x}} - 5} \right)\left( {2{\rm{x}} + 7} \right) = 0\\
\Leftrightarrow \left( {2{\rm{x}} - 5} \right)\left( {2{\rm{x}} + 5 - 2{\rm{x}} - 7} \right) = 0\\
\Leftrightarrow \left( {2{\rm{x}} - 5} \right)\left( { - 2} \right) = 0\\
\Leftrightarrow 2{\rm{x}} - 5 = 0\\
\Leftrightarrow 2{\rm{x}} = 5\\
\Leftrightarrow x = \frac{5}{2}\\
Vay:x = \frac{5}{2}\\
c){\rm{ }}{x^2} - 9x + 8 = 0\\
\Leftrightarrow {x^2} - x - 8{\rm{x}} + 8 = 0\\
\Leftrightarrow x\left( {x - 1} \right) - 8\left( {x - 1} \right) = 0\\
\Leftrightarrow \left( {x - 1} \right)\left( {x - 8} \right) = 0\\
\Leftrightarrow \left[ \begin{array}{l}
x - 1 = 0\\
x - 8 = 0
\end{array} \right.\\
\Leftrightarrow \left[ \begin{array}{l}
x = 1\\
x = 8
\end{array} \right.\\
Vay:S = \{ 1;8\}
\end{array}\]

...Xem thêm

Answer 2

\[\begin{array}{l}
\;a){\rm{ }}{x^3} - {\rm{ }}9x = 0.\\
\Leftrightarrow x\left( {{x^2} - 9} \right) = 0\\
\Leftrightarrow x\left( {x - 3} \right)\left( {x + 3} \right) = 0\\
\Leftrightarrow \left[ \begin{array}{l}
x = 0\\
x - 3 = 0\\
x + 3 = 0
\end{array} \right.\\
\Leftrightarrow \left[ \begin{array}{l}
x = 0\\
x = 3\\
x = - 3
\end{array} \right.\\
vay:S = \{ 0; - 3;3\} \\
b){\rm{ }}4{x^2} - 25 - \left( {2x - 5} \right)\left( {2x + 7} \right) = 0\\
\Leftrightarrow \left( {4{{\rm{x}}^2} - 25} \right) - \left( {2{\rm{x}} - 5} \right)\left( {2{\rm{x}} + 7} \right) = 0\\
\Leftrightarrow \left( {2{\rm{x}} - 5} \right)\left( {2{\rm{x}} + 5} \right) - \left( {2{\rm{x}} - 5} \right)\left( {2{\rm{x}} + 7} \right) = 0\\
\Leftrightarrow \left( {2{\rm{x}} - 5} \right)\left( {2{\rm{x}} + 5 - 2{\rm{x}} - 7} \right) = 0\\
\Leftrightarrow \left( {2{\rm{x}} - 5} \right)\left( { - 2} \right) = 0\\
\Leftrightarrow 2{\rm{x}} - 5 = 0\\
\Leftrightarrow 2{\rm{x}} = 5\\
\Leftrightarrow x = \frac{5}{2}\\
Vay:x = \frac{5}{2}\\
c){\rm{ }}{x^2} - 9x + 8 = 0\\
\Leftrightarrow {x^2} - x - 8{\rm{x}} + 8 = 0\\
\Leftrightarrow x\left( {x - 1} \right) - 8\left( {x - 1} \right) = 0\\
\Leftrightarrow \left( {x - 1} \right)\left( {x - 8} \right) = 0\\
\Leftrightarrow \left[ \begin{array}{l}
x - 1 = 0\\
x - 8 = 0
\end{array} \right.\\
\Leftrightarrow \left[ \begin{array}{l}
x = 1\\
x = 8
\end{array} \right.\\
Vay:S = \{ 1;8\}
\end{array}\]

1 câu trả lời 389

Câu hỏi hot cùng chủ đề

Bài viết mới nhất Lớp 8