5X²-2=（√5x+√2)(√5x-√2)
x四次方-4x²+4
=(x²-2)²
=(x+√2)²(x-√2)²
x四次方+2x²-8
=(x²+4)(x²-2)
=(x²+4)(x+√2)(x-√2)
x五次方-3x三次方-10x
=x(x^4-3x^2-10)
=x(x²-5)(x²+2)
=x(x+√5)(x-√5)(x²+2)