Given the anodes are connected together, the grids are connected together and the cathodes are connected together i.e. two triodes have same voltage and same current which means r_P1 = r_P2=r

Here the equivalent resistance,

i.e., the equivalent plate resistance is half to the individual plate resistance.

Let g_m1 and g_m2 be the individual conductance.

From figure, g_m1 = g_{m1 =} g. As two triodes are parallel i.e. equivalent conductance

i.e. The equivalent mutual conductance is double the individual mutual conductance

Now,

Also,

I.e. the equivalent amplification factor is the same as the individual amplification factor