Yes, 三角学助手 - 解题器 is completely free and it doesn't have any in-app purchases or subscriptions.
Not enough reviews to make a reliable assessment. The app needs more user feedback.
三角学助手 - 解题器 is free.
To get estimated revenue of 三角学助手 - 解题器 app and other AppStore insights you can sign up to AppTail Mobile Analytics Platform.