Write about severity of the problem "Flurorosis" in A.P.?

S_n in A.P.=

if a, b,c are in A.P. then b =

Find the 11^(th) term from the last of the A.P series given below: A.P : 10, 7, 4, ......, -62

Write the formula for finding number of terms in A.P

In an A.P. the common difference (d) is 6 and seventh term is 36. Can we write such an A.P.?

Show that the solutions Cos p theta = Sin q theta from two series each of which is an A.P. Find also the common difference of each A.P (p ne pm q)