Draw (a+b)^2 only as reference

first confusion: triangle, draw squares ask why should they be equal, then draw the (a+b)^2 as a square reference frame, then on one side of the equal you fill in a^2 and b^2 and on the other side c^2 and then tune in why they are equal

ayla/zidane could point out that its the same trick as it was with the cupboard that we can seperate a rectangle here a*b into two rectangular triangles