[填空题]
The following diagram sowg/3)qs q(eo hows the (cwq; p(6c yhvw4x dw*curve y=a sin (k(x-d))+c where a, k, d and c are all positive consyw(pxh; cc w( d4v*w6qtants. 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 .
