当n=无穷大时,角bic趋于180度.
∠bic=∠a+1/2(∠b+∠c)+1/4(∠b+∠c)+1/8(∠b+∠c)+.+1/(n-2)(∠b+∠c)+1/(n-1)(∠b+∠c)+1/n(∠b+∠c)趋于180度