观察式子：(1/(1*3))=(1/2)(1-(1/3))，(1/(3*5))=(1/2)((1/3)-(1/5))，(1/(5*7))=(1/2)((1/5)-(1/7))，…．由此计算：(1/(1*3))+(1/(3*5))+(1/(5*7))+…+(1/(2009*2011))=多少． equation:x=(1/2)*(1-(1/2011)) (1005/2011) 水水家离学校200米