help aaaaaaaaaaaaaaaaaaaaaaaaaaaa

a) `x^4-16x^2=0`

`=> x^2(x^2-16)=0`

TH1:

`x^2=0`

`=> x=0`

TH2:

`x^2-16=0`

`=> x^2=16`

`=> x=±4`

Vậy `x={0; 4; -4}`

b) `x^8+36x^4=0`

`=> x^4(x^2+36)=0`

TH1:

`x^4=0`

`=> x=0`

TH2:

`x^2+36=0`

`=> x^2=-36` (vô lí)

`->` Loại

Vậy `x=0`