(a) If $\mathrm{x}, \mathrm{y}, \mathrm{z}$ be respectively $\mathrm{AM}, \mathrm{GM}, \mathrm{HM}$ between two rational numbers
(p) $\frac{a+b}{a b}$
a and $\mathrm{b}$ then $\mathrm{x}-\mathrm{y}$ is equal to
(b) If $\mathrm{A}_{1}, \mathrm{~A}_{2}$ be two AMs and $\mathrm{G}_{1}, \mathrm{G}_{2}$ be two GMs; between a and $\mathrm{b}$, then
(q) $\left(\frac{\sqrt{a}-\sqrt{b}}{\sqrt{2}}\right)^{2}$
$\frac{\mathrm{A}_{1}+\mathrm{A}_{2}}{\mathrm{G}_{1} \mathrm{G}_{2}}$ is equal to
(c) If $\mathrm{A}_{1}, \mathrm{~A}_{2}$ be two $\mathrm{AMs} ; \mathrm{G}_{1}, \mathrm{G}_{2}$ be two $\mathrm{GMs} ; \mathrm{H}_{1}, \mathrm{H}_{2}$ be two $\mathrm{HMs}$ between
(r) $\frac{a b}{a+b}$
two positive numbers a and b, then $\frac{\mathrm{G}_{1} \mathrm{G}_{2}}{\mathrm{H}_{1} \mathrm{H}_{2}} \frac{\mathrm{H}_{1}+\mathrm{H}_{2}}{\mathrm{~A}_{1}+\mathrm{A}_{2}}$
(d) If $\mathrm{A}_{1}, \mathrm{~A}_{2}$ be two $\mathrm{AMs} \mathrm{G}_{1}, \mathrm{G}_{2}$ be two $\mathrm{GMs} \mathrm{H}_{1}, \mathrm{H}_{2}$ be two $\mathrm{HMs}$ between
(s) 1 two numbers a and b, then $\frac{1}{\mathrm{H}_{1}}+\frac{1}{\mathrm{H}_{2}}$ is equal to