$6\mathrm{.}10$ Difference amplifiers are often used in conjunction with a Wheatstone bridge, such as that shown in Figure P$6\mathrm{.}10,$ where each resistor is a temperature sensing element, and their change in resistance $R$ is directly proportional to their change in temperature $T.$ The constant of proportionality is the temperature coefficient $+-,$ which can be positive $($PTC$)$ or negative $($NTC$).$ Find the Th$$venin equivalent network seen by the amplifier to the left of nodes a and $b.$ Assume that $R=+-T$ and $|R|R_0.$

Figure P$6\mathrm{.}10$