(called 0/0 type and ∞ /∞ type infinitives), the limit calculation can be done by' Robida's Law':

1，lim(x->； a)f(x)/g(x)= lim(x-& gt； a)f’(x)/g’(x)？

If lim (x->; A) f' (x)/g' (x) is still the infinitive 0/0 or ∞ /∞, and then come back.

Use the Rovida Method once:

2，lim(x-& gt； a)f(x)/g(x)= lim(x-& gt； a) f ''(x)/g ''(x)

Until you find the limit.

for instance

① find lim (x->; 0) sin x/x limit: when x->; 0, sin x/x, become 0/0 infinitive, using Roche's law:

lim(x->； 0)sin x/x = lim(x-& gt； 0) cos x / 1 = 1？

② find lim (x->; ∞) the limit of x 3/e x: when x->; ∞), x 3/e x, becomes ∞ /∞) infinitive, using Roche's law:

lim(x->； ∞)x^3/e^x = lim(x-& gt； ∞)3x^2/e^x = lim(x-& gt； ∞)6x/e^x = lim(x-& gt； ∞) 6/e^x = 0