So, I'm reading a physics book, and it talks about Newton's three laws, of course, but then after that it says that if a force of f pushes on an object at angle Θ, then the force in the x direction is f ⋅ cos(Θ), and the force in the y direction is f ⋅ sin(Θ). Where did THAT come from? Do we derive it from Newton's laws? Or is it just assumed, like an implicit fourth law? Or what? (Someone told me it was related to kinetic energy or something, but I don't understand.) Thanks.