@Sawarnik A regular $12$ sided polygon is inscribed in a circle of radius $10$. $A, B, C, D, E$ are its consecutive vertices taken in that order. Find the area of quad. $ABDE$.
Since $BOD$ is equilateral, $BD=10$. The height of the trapezium (why?) $ABDE$ is $\frac{s}{\sqrt2}$ as $\angle BAE =45^{\circ}$, where $s$ is the side. So the area is, $\frac{s^2}2+5\sqrt2s$.
Nothing better, getting angles from the center and doing stuff. But leave it. If we an easily calculate ∠AMB where M is the intersection of diagonals, then there is a formula that is highly useful.
Chain rule is easy to remember, its the quotient rule that I never remember. And yeah, sin(a+b) and cos(a+b) and sina+sinb and tan(2a) and .....................
@ParthKohli Sometimes when you overstudy maths gets boring.
