$x^{4}$ -13x²+36=0
(=)$x^{4}$-9x²-4x²+36=0
(=)x²(x²-9)-4(x²-9)=0
(=)(x²-4)(x²-9)=0
(=)\(\left[ \begin{array}{l}x²-4=0\\x²-9=0\end{array} \right.\) (=)\(\left[ \begin{array}{l}x²=4\\x²=9\end{array} \right.\) (=)\(\left[ \begin{array}{l}x=±2\\x=±3\end{array} \right.\)
9$x^{4}$+6x²+1=0
(=)(3x²+1)²=0
(=)3x²+1=0
(=)3x²=-1 =) vô lý
x²-11x+30=3
(=)x²-11x+30-3=0
(=)x²-11x+27=0
- x =(11-√13)/2= 3.697
- x =(11+√13)/2= 7.30
x²-4x+2=0
(=)x²-4x=-2
(=)x²-4x+4=-2+4
(=)√(x-2)²=2
(=)x-2=±√2
(=)x=2±√2
