For the problem of 5)7), the direct numerator denominator is divided by the highest power at the same time, for example, the seventh power is a square term, and the numerator denominator is divided by x? , so there is lim( 1+3/x? ) /(3-2/x), when x is infinite, 1/x? And 1/x tends to 0, so this limit =1/3;

no . 10)lim( 1/( 1-x)- 1/( 1-x 3))= lim( 1+x+x？ -3)/(( 1-x)( 1+x+x？ ))

= lim(x- 1)(x+2)/(( 1-x)( 1+x+x？ ))=-lim(x+2)/( 1+x+x？ )=-3/3=- 1

No. 14) can't be seen clearly. Just divide the denominator by the highest power of x.

15) 16) This kind of question requires that the denominator is physical and chemical or the molecule is physical and chemical, for example, 15) The denominator of the molecule is multiplied by √(x? +x-2)+√(x？ -2x-2), then the original limit =lim[√(x? +x-2)+√(x？ -2x-2)]/[3x], and then the numerator and denominator are divided by x at the same time to get the limit of 2/3.