2.38 A weighted summer circuit using an ideal op amp as shown in Fig. 2.10 has three inputs using 20- kΩ resistors and a feedback resistor of 50 kΩ. A signal v1 is connected to two of the inputs while a signal v2 is connected to the third. Express vO in terms of v1 and v2. If v1 = 1 V and v2 = −1 V, what is vO?