a) \(\left(5x+2\right)\left(x-7\right)=0\)
\(\Leftrightarrow5x+2=0\) hoặc \(x-7=0\)
*) \(5x+2=0\)
\(\Leftrightarrow x=\dfrac{-2}{5}\)
*) \(x-7=0\)
\(\Leftrightarrow x=7\)
Vậy \(S=\left\{\dfrac{-2}{5};7\right\}\)
b) \(15\left(x+9\right)\left(x-3\right)\left(x+12\right)=0\)
\(\Leftrightarrow x+9=0\) hoặc \(x-3=0\) hoặc \(x+12=0\)
*) \(x+9=0\)
\(\Leftrightarrow x=-9\)
*) \(x-3=0\)
\(\Leftrightarrow x=3\)
*) \(x+12=0\)
\(\Leftrightarrow x=-12\)
Vậy \(S=\left\{-12;-9;3\right\}\)
c) \(x^2-x-6=0\)
\(\Leftrightarrow x^2+2x-3x-6=0\)
\(\Leftrightarrow\left(x^2+2x\right)-\left(3x+6\right)=0\)
\(\Leftrightarrow x\left(x+2\right)-3\left(x+2\right)=0\)
\(\Leftrightarrow\left(x+2\right)\left(x-3\right)=0\)
\(\Leftrightarrow x+2=0\) hoặc \(x-3=0\)
*) \(x+2=0\)
\(\Leftrightarrow x=-2\)
*) \(x-3=0\)
\(\Leftrightarrow x=3\)
Vậy \(S=\left\{-2;3\right\}\)
d) \(4x^2\left(3x-7\right)=16\left(3x-7\right)\)
\(\Leftrightarrow4x^2\left(3x-7\right)-16\left(3x-7\right)=0\)
\(\Leftrightarrow\left(3x-7\right)\left(4x^2-16\right)=0\)
\(\Leftrightarrow\left(3x-7\right)\left(2x+4\right)\left(2x-4\right)=0\)
\(\Leftrightarrow3x-7=0\) hoặc \(2x+4=0\) hoặc \(2x-4=0\)
*) \(3x-7=0\)
\(\Leftrightarrow3x=7\)
\(\Leftrightarrow x=\dfrac{7}{3}\)
*) \(2x+4=0\)
\(\Leftrightarrow2x=-4\)
\(\Leftrightarrow x=-2\)
*) \(2x-4=0\)
\(\Leftrightarrow2x=4\)
\(\Leftrightarrow x=2\)
Vậy \(S=\left\{-2;2;\dfrac{7}{3}\right\}\)
giải hộ mình mấy bài này vs ạ !
