If `a , b , c ,d` and `p` are distinct real numbers such that (1987, 2M) `(a^2+b^2+c^2)p^2-2(a b+b c+c d)P+(b^2+c^2+d^2)geq0,t h e na , b , c , d` are in AP (b) are in GP are in HP (d) satisfy `a b=c d`