Too late to edit now, but wanted to add a note: Knowing that cos(45) == sqrt(2)/2 seems like something you would need to memorize, but if you just draw an isos

Too late to edit now, but wanted to add a note: Knowing that cos(45) == sqrt(2)/2 seems like something you would need to memorize, but if you just draw an isosceles right triangle with sides equal to 1 and use the Pythagorean Theorem you'll find that the hypotenuse is sqrt(2)/2.