Question

Bài 6: Giải các phương trình sau:

4)

6)

11) 

12) 

13) 

Answer 1

`x(x-1)(x+1)(x+2)=24`

`<=>[x(x+1)][(x-1)(x+2)]=24`

`<=>(x^2+x)(x^2+x-2)=24`

`<=>(x^2+x-1)^2=25`

`+)x^2+x-1=5`

`<=>x^2+x-6=0`

`<=>x^2-2x+3x-6=0`

`<=>x(x-2)+3(x-2)=0`

`<=>(x-2)(x+3)=0`

`<=>` $\left[ \begin{array}{l}x=2\\x=-3\end{array} \right.$

`+)x^2+x-1=-5`

`<=>x^2+x+4=0`

`<=>(x+1/2)^2+15/4=0` vô lý

Vậy `S={2,3}`

Answer 2

`11)4x^2+4-8x=9(x-2)^2`

`<=>4(x^2-2x+1)=9(x-2)^2`

`<=>(2x-2)^2=(3x-6)^2`

`<=>(3x-6-2x+2)(3x-6+2x-2)=0`

`<=>(x-4)(5x-8)=0`

`<=>` $\left[ \begin{array}{l}x=4\\x=\dfrac{8}{5}\end{array} \right.$

Vậy `S={4,5/8}`