If PQR is a triangle of area Δ with a = 2, b = 7/2, and c = 5/2, where a, b and c are the lengths of the sides of the triangle opposite to the angles at P, Q and R respectively, then \(\frac{2\sin P - \sin 2P}{2\sin P + \sin 2P}\) equals
If \(a_1, a_2, a_3, \ldots, a_n\) are in AP with common difference \(5\) and if \(a_i a_j \neq -1\) for \(i, j = 1, 2, \ldots, n\), then \(\tan^{-1}\left(\frac{5}{1 + a_1 a_2}\right) + \tan^{-1}\left(\frac{5}{1 + a_2 a_3}\right) + \tan^{-1}\left(\frac{5}{1 + a_{n-1}a_n}\right) + \ldots + \tan^{-1}\left(\frac{5}{1 + a_n a_1}\right)\) is equal to