$2\mathrm{.}63$ Find the voltage gain $v_O{v}_{ld}$ for the difference amplifier of Fig. $2\mathrm{.}16$ for the case $R_1=R_3=5k$ and $R_2=R_4=50k.$ What is the differential input resistance $R_{id}?$ If the two key resistance ratios $(\frac{R_2}{R_1})$ and $(\frac{R_4}{R_3})$ are different from each other by $1\%,$ what do you expect the common$-$mode gain $A_{cm}$ to be$?$ Also, find the CMRR in this case. Neglect the effect of the ratio mismatch on the value of $A_d.$