Giải phương trình a)x^2+2x=15 b)2x^3-2x^2=4x c)x^4-5x^3+4x^2=0 d)x^3+4x^2-9x-36=0 Vote 5 sao nè

a) x²+2x=15

⇔x²+2x-15=0

⇔x²-3x+5x-15=0

⇔x(x-3)+5(x-3)=0

⇔(x-3)(x+5)=0

⇔\(\left[ \begin{array}{l}x-3=0\\x+5=0\end{array} \right.\) =>\(\left[ \begin{array}{l}x=3\\x=-5\end{array} \right.\) 

Vậy S={3;-5}

b)2x³-2x²=4x

⇔2x³-2x²-4x=0

⇔2x(x²-x-2)=0

⇔2x(x-2)(x+1)=0

⇔x=0; x=2; x=-1

Vậy S={0;2;-1}

c)x^4-5x³+4x²=0

⇔x²(x²-5x+4)=0

⇔x²(x-1)(x-4)=0

⇔x=0;x=1;x=4

Vậy S={0;1;4}

d)x³+4x²-9x-36=0

⇔x²(x+4)-9(x+4)=0

⇔(x+4)(x-3)(x+3)=0

⇔x=-4;x=±3

Vậy S={-4;±3}