分式(x²+2x+1)/(4x²-7x+4)的分子与分母都除以x得到
(x²+2x+1)/(4x²-7x+4)
=(x+2+1/x)/(4x-7+4/x)
=[(x+1/x)+2]/[4(x+1/x)-7]
=[2+2]/[4*2-7]
=4