=1/2(x^4-10x^2+9)=1/2(x^2-9)(x^2-1)=1/2(x-3)(x+3)(x-1)(x+1)
1/2x^4-5x^2+9/2 =1/2(x^4-10x²+9)=1/2(x²-1)(x²-9)=1/2(x+1)(x-1)(x+3)(x-3)
1/2(x-3)(x+3)(x-1)(x+1)
