[填空题]
The following diagram shkag yz+e04 k7flee4ij7 ;+esn ow7lsf f(plt*u+ s the curve y=a sin (k(x-d))+c where a, k, d and c are all positive constants. The curve has a minimum point at (1.5,1lptf f7 (slu*+) 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 .
