You can check that both firms are then playing a best response, so that's all right.

你们可以验证,两家公司都进行了最佳对策,那是正确的

耶鲁公开课 - 博弈论课程节选

The reason is that the best response for Firm 1, So it turns out it's pretty to check that this is the only Nash Equilibrium in the game.

因为公司1的最佳对策,所以很容易验证,这是此博弈中唯一的纳什均衡

耶鲁公开课 - 博弈论课程节选