lim(x→1）[(5x-4)的平方根-(x)的平方根]/(X-1)
=lim(x→1）(5x-4-x)/(x-1)(√5x-4+√x)
=lim(x→1）(4x-4)/(x-1)(√5x-4+√x)
=lim(x→1）4/(√5x-4+√x)
=4/(√5-4+1)
=4/(1+1)
=2