`e)2(x+5)-x^2-5x=0`
`<=>2(x+5)-x(x+5)=0`
`<=>(2-x)(x+5)=0`
`<=>2-x=0` hoặc `x+5=0`
`<=>x=2` hoặc `x=-5`
`f)6x^2+13x+5=0`
`<=>(6x^2+6x)+(5x+5)=0`
`<=>6x(x+1)+5(x+1)=0`
`<=>(x+1)(6x+5)=0`
`<=>x+1=0` hoặc `6x+5=0`
`<=>x=-1` hoặc `x=-5/6`
`g)15x^2+11x-12=0`
`<=>(15x^2-9x)+(20x-12)=0`
`<=>3x(5x-3)+4(5x-3)=0`
`<=>(5x-3)(3x+4)=0`
`<=>5x-3=0` hoặc `3x+4=0`
`<=>x=3/5` hoặc `x=-4/3`
`h)5-6x+x^2=0`
`<=>(x^2-x)+(-5x+5)=0`
`<=>x(x-1)-5(x-1)=0`
`<=>(x-1)(x-5)=0`
`<=>x-1=0` hoặc `x-5=0`
`<=>x=1` hoặc `x=5`
i) `2x^3-16x=0`
`<=>2x(x^2-8)=0`
`<=>2x=0` hoặc `x^2-8=0`
`<=>x=0` hoặc \(x=\pm2\sqrt{2}\)
a: \(4x^2+15x=25\)
=>\(4x^2+15x-25=0\)
=>\(4x^2+20x-5x-25=0\)
=>4x(x+5)-5(x+5)=0
=>(x+5)(4x-5)=0
=>\(\left[{}\begin{matrix}x+5=0\\4x-5=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=-5\\x=\dfrac{5}{4}\end{matrix}\right.\)
b: \(x^3+x^2=36\)
=>\(x^3+x^2-36=0\)
=>\(x^3-3x^2+3x^2-12x+12x-36=0\)
=>\(x^2\left(x-3\right)+3x\left(x-3\right)+12\left(x-3\right)=0\)
=>\(\left(x-3\right)\left(x^2+3x+12\right)=0\)
mà \(x^2+3x+12=\left(x+\dfrac{3}{2}\right)^2+9,75>=9,75\forall x\)
nên x-3=0
=>x=3
c: \(x^3-4x=0\)
=>\(x\left(x^2-4\right)=0\)
=>x(x-2)(x+2)=0
=>\(\left[{}\begin{matrix}x=0\\x-2=0\\x+2=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=0\\x=2\\x=-2\end{matrix}\right.\)
d: 5x(x-1)=x-1
=>5x(x-1)-(x-1)=0
=>(x-1)(5x-1)=0
=>\(\left[{}\begin{matrix}x-1=0\\5x-1=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=1\\x=\dfrac{1}{5}\end{matrix}\right.\)
