1. I bought the book, which was good to use.

2. I bought the book, and it was good to use.

3. I bought the book, being good to use.
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What about this one? Is #3 grammatical?

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4. He hit the ball, and it flew up.
5. He hit the ball, which flew up.
6. He hit the ball, flying up.
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What about these three sentences? Are they all grammatical? Can we use Sentence 6? Does #4 mean #6? Or did he flew up while he hit the ball?

Again, the -ing phrasing is not the best. It's not incorrect; it's just not used very much.

1, 2, 4, and 5 are the best sentences here.