1/2(1+1/2)(1+1/4)(1+1/16) =（1-1/2)(1+1/2)(1+1/4)(1+1/16) =1/4(1+1/4)(1+1/16) =(1-1/4)(1+1/4)(1+1/16) =1/16(1+1/16) =(1-1/16)(1+1/16) =1/256