Question

He failed he was unlucky combine into one simple sentence

Answer 1

He failed in a exam and un lucky.

I think it's correct answer.

Answer 2

He failed as he was unlucky.

This is the right form of the sentence as the conjunction used combines the two different phrases into one single sentence to give it an appropriate meaning by keeping the originality of the sentence intact.

The word "as" is used here to join the sentence.