例：1/2+1/4+1/8+1/16+……+1/2^n……设1/2+1/4+1/8+1/16+……+1/2^n……=a,因为此为无限收敛级数,所以2a=1+1/2+1/4+1/8+1/16+……+1/2^n……,而a=2a-a=1+1/2+1/4+1/8+1/16+……+1/2^n……-(1/2+1/4+1/8+1/16+……+1...