Hello, I am totally bad at geometry , by geometry I mean plane euclidean geometry with similarities and circles. I sometimes feel totally lost with problems. For example: The parallel sides of trapezoid ABCD are 3 cm and 9 cm(AB and DC).The non parallel sides are 4 cm and 6 cm(AD and BC).A line(PQ) parallel to base(DC) divides the trapezoid into two trapezoids(ABQP and PQCD ) of equal perimeters. Find the ratio in which each of the non parallel sides is divided I knew that this problem had to do with the Thales theorem but I felt completely lost after equating perimeters. So my question is can someone recommend a book / videos (anything!) to improve plane geometry? Moreover since I plan on studying Physics, is euclidean geometry needed in Physics? Thanks in advance.