Câu hỏi của Thảo Công Túa

Question

giải phương trình

a) $\left(5x+2\right)\left(x-7\right)=0$

b) $\left(x^2-1\right)\left(x+3\right)=0$

c) $x^2-x-6=0$

d) $x^2+x-12=0$

e) \(15\left(x+9\right)\left(x-3\right)\left(x+21\right...

Võ Đông Anh Tuấn · Accepted Answer

a ) $\left(5x+7\right)\left(x-7\right)=0$

$\Leftrightarrow\left[{}\begin{matrix}x=-\dfrac{7}{5}\x=7\end{matrix}\right.$

b ) $\left(x^2-1\right)\left(x+3\right)=0$

$\Leftrightarrow\left(x-1\right)\left(x+1\right)\left(x+3\right)=0$

$\Leftrightarrow\left[{}\begin{matrix}x=1\x=-1\x=-3\end{matrix}\right.$

c )$x^2-x-6=0$

$\Leftrightarrow x^2-3x+2x-6=0$

$\Leftrightarrow\left(x+2\right)\left(x-3\right)=0$

$\Leftrightarrow\left[{}\begin{matrix}x=-2\x=3\end{matrix}\right.$

d ) $x^2+x-12=0$

$\Leftrightarrow x^2-4x+3x-12$

$\Leftrightarrow\left(x+3\right)\left(x-4\right)=0$

$\Leftrightarrow\left[{}\begin{matrix}x=-3\x=4\end{matrix}\right.$

e ) $15\left(x+9\right)\left(x-3\right)\left(x+21\right)=0$

$\Leftrightarrow\left[{}\begin{matrix}x=-9\x=3\x=-21\end{matrix}\right.$

g ) $\left(x^2+1\right)\left(x^2+4x+4\right)=0$

$\Leftrightarrow\left(x^2+1\right)\left(x+2\right)^2=0$

$\Leftrightarrow\left[{}\begin{matrix}x^2=-1\left(loại\right)\x=-2\end{matrix}\right.$

i ) $x^4+2x^3-2x^2+2x-3=0$

$\Leftrightarrow x^4+3x^3-x^3-3x^2+x^2+3x-x-3=0$

$\Leftrightarrow x^3\left(x+3\right)-x^2\left(x+3\right)+x\left(x+3\right)-\left(x+3\right)=0$

$\Leftrightarrow\left(x^3-x^2+x-1\right)\left(x+3\right)=0$

$\Leftrightarrow\left(x^2+1\right)\left(x-1\right)\left(x+3\right)=0$

$\Leftrightarrow\left[{}\begin{matrix}x^2=-1\left(loại\right)\x=1\x=-3\end{matrix}\right.$

h) $x^2+5x+6=0$

$\Leftrightarrow x^2+3x+2x+6=0$

$\Leftrightarrow\left(x+2\right)\left(x+3\right)=0$

$\Leftrightarrow\left[{}\begin{matrix}x=-2\x=-3\end{matrix}\right.$Câu trả lời: a ) $\left(5x+7\right)\left(x-7\right)=0$