LawOfCosines
PlaneGeometry
Intermediate
Let $ABCD$ be inscribed in a circle. If $AB=a, BC=b, CD=c,$ and $DA=d$, show that $$\cos{B} = \frac{a^2 + b^2 -c^2 - d^2}{2(ab+cd)}$$
The solution for this problem is available for
$0.99.
You can also purchase a pass for all available solutions for
$99.