How to win this 2 rook vs 2 rook endgame?

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sta202020

This positon came from a game I palyed with a chess.com bot. I was black, I chose to get a draw  by perpetual check.

According to the engine,Black has a winning position,but I cannot understand the main idea,can  anybody explain to me? 

Thank you in advance!

sta202020
1832870982 写道:

it's a draw position for both sides at all,so if there is a great disparity in strength between the two sides,the continuous check to accept a draw would be best result

got it 

thank you