he had racked his brain meaning in English

他已绞尽了脑汁

He had racked his brain
他可是个有头脑的人。
He had racked his brain . / he ' s a brain . / li ming has a lot on the ball
他绞尽乐脑汁。 /他可是个有头脑的人。 /李明很能干。
He had racked his brain , but he still couldn ' t work out the answer to the problem
他已经绞尽脑汁了，可是仍未找出问题的答案。
He had racked his brain , but hadn ' t been able to work out the answer to the problem
他已经绞尽脑汁了，可是仍未找到问题的答案。
3 he had racked his brain , but hadn ' t been able to work out the answer to the problem
他已经绞尽脑汁了,但还是没有想出这个问题的答案