題組內容

1. 設 f (x,y)=xy, x(t)=cost , y(t)=sint, g(t)=f(x(t),y(t)), t∈(-∞,∞ )

(ii) (the differential ) df = ? (用 dx, dy 回答)；用 chain rule 計算出 dg = ? (用 dt 回答)