[填空题]
The following diagra xr0bu1*bm .ha)-uyhua f3 t/- vkhyc0m shows the curve y=a sin (k(x-d))+c where a, k, d and c ah)0vk3t-u ycuf-/a yh re all positive constants. The 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 .
