2x三次+x分之1-4x四次方
=(1+2x²)(1-2x²)/[x(2x²+1)]
=(1-2x²)/x
y-x平方y分之x平方y-2xy+y
=y(x-1)²/[y(1+x)(1-x)]
=(1-x)/(1+x)
a平方-6ab+9b平方分之a平方-3ab
=a(a-3b)/[(a-3b)²
=a/(a-3b)