Problem 15 (trigonometry): Always observe the answer options before you start to work on a problem. For example, if the answer options show bounds, then don’t go ahead and try to calculate the actual value. Problem 16 (circles): Descartes’ Circle Theorem states that $2(a^2 + b^2 + c^2 + d^2)=(a+b+c+d)^2$,…
