Why is the direct object incorrect in this sentence?

Question

In the following statement, the direct object "them" is incorrect and should be removed. Why?

I believe that all the principles that underlie how a radio works are beneficial to use them in other invention.

Answer 1

Welcome, I am also an English learner. I may happen to know you question.

This is actually about the usage of infinitives.

Let's peel away the unnecessary part(modifiers） of your sentence:

I believe that all the principles are beneficial to use them.

Here the logic object of infinitive "to use" is "all the principles", so it is redundant to mention it again by using "them". Deleting it, you can write it another way:

I believe that to use all the principles are beneficial.