If $\frac{a}{b + c}, \frac{b}{c + a}, \frac{c}{a + b}$ are in $H.P.$,then $a, b, c$ are in

If $a, b, c$ are in $H.P.$,then for all $n \in N$ $(n > 1)$,the true statement is:

If $p, q, r$ are in harmonic progression and $p$ and $r$ are distinct and have the same sign,then what is the nature of the roots of the equation $px^2 + 2qx + r = 0$?

If for the series $a_1, a_2, a_3, \ldots$, the expression $a_r - a_{r+1}$ bears a constant ratio with $a_r a_{r+1}$, then $a_1, a_2, a_3, \ldots$ are in:

Let $a_1, a_2, a_3, \dots$ be a harmonic progression where $a_1 = 5$ and $a_{20} = 25$. What is the smallest positive integer $n$ such that $a_n < 0$?

If $\frac{a}{b}, \frac{b}{c}, \frac{c}{a}$ are in $H.P.$,then