Definition
used to express agreement to a proposed action or challenge
（表示同意） 好！就这么定了！
"I bet I can run this lap in under ten minutes." "You're on!"
「我赌我能在十分钟内跑完这圈。」「好！就这么定了！」
"Let's have a race to see who can finish this report first." "You're on!"
「我们来比赛看谁能先完成这份报告。」「好！就这么定了！」
"If you can complete that project, I'll treat you to dinner." "You're on!"
「如果你能完成那个项目，我就请你吃晚餐。」「好！就这么定了！」