It's worth much more than I paid for it.为什么不用worthwhileThe doctor decided it would not be worthwhile to continue the treament.为什么用worthwhile不用worthy

1。意思是：它比我付出的代价值多了。。说的是价值，不是值得不值得
2。意思是：医生认为继续治疗已经不值得了。 是不值得去做了的意思，比worthy更确切

worth表示“值……钱,值得……的”
句子It's worth much more than I paid for it. 表示的是这件物品值很多钱,超过了我的支付能力.该句如果使用worthwhile就错了.
worthwhile表示“值得的”,一般可作定语和表语. 句子“The doctor decided it would not be worthwhile to continue the treament”表示医生认为已经不值得对病人继续进行处理或医治.
worthwhile的常用句式：
be worthwhile doing be worthwhile to do
worthy表示的是“有价值的,可尊敬的”,常作定语.如：The teacher was a worthy man.(那位老师是可尊敬的人),同时也可以表示“值得的”.如：The man is worthy of praise.(这人值得称赞)
常用句式 be worthy to be done
be worth doing、be worthy of being done
be worthy of + 名词

第二句话可以用whorthy,但其主语不能用it,也不能是医生,应改为the ill person等.