a) $x^{4}$ - 4x³ = 0
⇔ x³( x - 4 ) = 0
⇔ \(\left[ \begin{array}{l}x=0\\x=4\end{array} \right.\)
c) x³ + 6x² + 3x - 10 = 0
⇔ x³ - x² + 7x² - 7x + 10x - 10 = 0
⇔ x²( x - 1 ) + 7x( x - 1 ) + 10( x - 1 ) = 0
⇔ ( x² + 7x + 10 )( x - 1 ) = 0
⇔ ( x² + 2x + 5x + 10 )( x - 1 ) = 0
⇔ [ x( x + 2 ) + 5( x + 2 ) ]( x - 1 ) = 0
⇔ ( x + 2 )( x + 5 )( x - 1 ) = 0
⇔\(\left[ \begin{array}{l}x=-2\\x=-5\\x=1\end{array} \right.\)
e) $x^{4}$ + 5x³ + 15x - 9 = 0
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