解：(2^9)-(2^8)+(2^7)-(2^6)+(2^5)-(2^4)+(2^3)-(2^2)+2=(2^9)×[1-(-1/2)^9]/[1-(-1/2)]=512×[1+(1/512)]/(3/2)=512×(513/512)×(2/3)=513×(2/3)=171×2=342
