若<img src="https://static.pphuashu.com/wangke/imgs/topic/6c45ee176af80f087e603506c089bd21.png.png"/>和<img src="https://static.zxtiku.com/wangke/imgs/topic/b2c73d359a576ae4ee9c953514d72eed.png"/>都收敛，则<img src="https://static.zxtiku.com/wangke/imgs/topic/02126f483f035d5ea58a479a264abd6b.png"/>收敛