Here’s a list of math tips and tricks you can use that make some difficult problems trivial. They seem to work pretty well, though as some of the comments have revealed one or two of the shortcuts do not work in some situations. Still very useful though.
Speaking of math, here are some very beautiful items from the math realm. Shapes are important. These beauties are rather small and pricey. The process of making them is complicated, so there is some justification as to the pricing. I really wish they were much larger and a bit cheaper, though.