已知点B1(1,1) A1﹙0,1﹚∈y=kx+b b=1
B2(3,2),A2﹙1,2﹚∈y=kx+1 k=1
设Cn﹙an.0﹚ 则an=2^n-1
Bn﹙an,﹙an+1﹚/2﹚
B7的坐标是﹙127,64﹚