Cách giải:
`1,x^2-13x^2+36=0`
`->x^2-9x^2-4x^2+36=0`
`->x^2(x^2-9)-4(x^2-9)=0`
`->(x^2-9)(x^2-4)=0`
`->` \(\left[ \begin{array}{l}x^2=4\\x^2=9\end{array} \right.\)
`->` \(\left[ \begin{array}{l}x=2\\x=-2\\x=3\\x=-3\end{array} \right.\)
`2,9x^4+6x^2+1=0`
`->(3x^2+1)^2=0`
`->` pt vô nghiệm
`3,2x^3+5x^2+2=0`
`->2x^4+4x^2+x^2+2=0`
`->2x^2(x^2+2)+x^2+2=0`
`->(x^2+2)(2x^2+1)=0`
`->` pt vô nghiệm
`4,2x^4-7x^2-4=0`
`->2x^2-8x^2+x^2-4=0`
`->2x^2(x^2-4)+x^2-4=0`
`->(x^2-4)(2x^2+1)=0`
`->x^2-4=0`
`->x^2=4`
`->` \(\left[ \begin{array}{l}x=2\\x=-2\end{array} \right.\)
`5,x^4-5x^2+4=0`
`->x^4-x^2-4x^2+4=0`
`->x^2(x^2-1)-4(x^2-1)=0`
`->(x^2-1)(x^2-4)=0`
`->` \(\left[ \begin{array}{l}x^2=4\\x^2=1\end{array} \right.\)
`->` \(\left[ \begin{array}{l}x=2\\x=-2\\x=1\\x=-1\end{array} \right.\)
