16x^3+156x^2=972 X係幾多 求請教?

Sol
16x^3+156x^2=972
16x^3+156x^2－972=0
4x^3+39x^2－243=0
4*(－3)^3+39*(－3)^2－243=0
－3為一根
4x^3+39x^2－243=0
(4x^3+12x^2)+(27x^2+81x)+(－81x－243)=0
4x^2(x+3)+27x(x+3)－81(x+3)=0
(4x^2+27x－81)(x+3)=0
(4x－9)(x+9)(x+3)=0
x=9/4 or x=－9 or x=－3

16x^3+156x^2=972
16x^3+156x^2-972=0
x=9/4 or x=-3 or x=-9