Найти радиусы rk первых пяти зон Френеля, если расстояние от источника света до волновой поверхности a=1 м, расстояние от волновой поверхности

I think that travelling by bike is the best way of travelling because it doesn’t pollute the environment and it is healthy. But you can’t get anywhere you want by bike. Sometimes it’s necessary to use other means of transport such as a car or a plane. Cars are fast and convenient but they pollute the air very much. As for the planes, they are convenient too but they pollute the air even more than cars. I think you have to get somewhere by plane only if it’s necessary.