解微積分2題(2)

(2)
lim(y->0) (sin3y cot5y) / (y cot4y)
=lim(y->0) (sin3y cos5y sin4y) / (y cos4y)(sin 5y)
=lim(y->0) [(3sin3y/3y) cos5y (4sin4y/y)] / [(cos4y)(5sin 5y/5y)]
=[(3) (1) (4)] / [(1)(5)]
=12/5


(4)
for g is continuous
g(-2+) = g(-2-)
-2 = b (-2*-2)
b= - 1 / 2