Let A,B,C and D be angles in a quadrilateral. Prove that:

**√**(CSinASinB)+**√**(ASinCSinD)+**√**(D|CosACosB|)+**√**(B|CosCCosD|) **≤** 2**√**(pi)

(In reply to

Solution by Praneeth)

You say:

You forgot to consider the case where the largest angle is

greater than 180.

I say: the largest angle is **N E V E R**

greater than 180.