How to get the coordinates of the vertices after rotating the rectangle?

Question

Mathematics

Good evening! I already have a headache. Help me please. The task is essentially school, from the point of view of mathematics.
In general, this is the task. There is a rectangle. The origin of coordinates is in its upper left corner, i.e. x1=0 y1=0
I know its height and width.
Here I rotate this rectangle by 45 or -45 degrees. I need to get the new coordinates of its vertices.
What for?? Everything is simple. There is an image. I rotate it by 45 and save it. And whatever it is cut off, you need to enlarge the canvas on which it lies, but so that the tops of the picture (which you turned over) lie on the edges of the canvas.
So that the picture is not cut off, and the canvas is exactly the same size, no more.
I almost forgot. Rotation about the center of the rectangle. But I think it's understandable
Выручайте! Жду ответа. Просто скажите формулы как пересчитать все 4 вершины прямоугольника. Спасибо

Answer 1

https://ru.wikipedia.org/wiki/%D0%A2%D1%80%D0%B8%D...