Question

嗯,我给难道了.求数学大神发功带我飞.

Answer 1

由x→a,lim[(f(x)-b)/(x-a)]=A可知

①x→a时f(x)→b

即f(a)=b;

②x→a时

lim[(f(x)-b)/(x-a)]

=limf'(x)=f'(a)=A

∴当x→a时

lim[(sinf(x)-sinb)/(x-a)]

=lim[(cosf(x)·f'(x)]

=cosf(a)·f'(a)

=Acos