[填空题]
The following diagram shd uw)g4:3 v(mwxgk3yhows the curve y=a sin (k(x-d))+c .jafy+2o hi1iwhere a, k, d and c are all positive constants. Thef1j.h2a + yioi curve has a minimum point at (1.5,1) and a maximum point at (3,7) .
1. Write down the value of a and the value of c . a = c =
2. Find the value of k .
3. Find the smallest possible value of d , given d>0 .
