Question

tìm x

a)x^2-x-12=0

b)x^2+3x-18=0

c)8x^2+30x+7=0

d)x^3-11x^2+30x=0

e)x^3-7x^2+15x-25=0

giúp mk vs ah!!!!!

Answer 1

Answer 2

a) Ta có: \(x^2-x-12=0\)

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

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

Answer 3

b) Ta có: \(x^2+3x-18=0\)

\(\Leftrightarrow\left(x+6\right)\left(x-3\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x=-6\\x=3\end{matrix}\right.\)

Answer 4

c) Ta có: \(8x^2+30x+7=0\)

\(\Leftrightarrow\left(4x+1\right)\left(2x+7\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x=-\dfrac{1}{4}\\x=\dfrac{-7}{2}\end{matrix}\right.\)

 

Answer 5

d) Ta có: \(x^3-11x^2+30x=0\)

\(\Leftrightarrow x\left(x-6\right)\left(x-5\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x=0\\x=6\\x=5\end{matrix}\right.\)

Answer 6

e) Ta có: \(x^3-7x^2+15x-25=0\)

\(\Leftrightarrow x^3-5x^2-2x^2+10x+5x-25=0\)

\(\Leftrightarrow x^2\left(x-5\right)-2x\left(x-5\right)+5\left(x-5\right)=0\)

\(\Leftrightarrow x-5=0\)

hay x=5