Find the thvenin equivalent this circuit over what portions

182	C H A P T E R	T H R E E

e x e r c i s e 3.21
a) Write in standard form the minimum number of node equations needed to analyze the circuit in Figure 3.122.

FIGURE 3.122	v		R1	R2	i4	R4
FIGURE 3.122	v		R1	R3	i4	R4

e x e r c i s e 3.22

FIGURE 3.123	a)	Find the Thévenin equivalent of the circuit in Figure 3.123.
		R3		I	R7
		R1	+-
FIGURE 3.124	b)	R2		R5	R8	A′

		R1		R2	1
		I			R4
		R3			1

A′

e x e r c i s e 3.25					a	2 V	- +
					b	2 V	- +

5 V	+ -	8kΩ
		8kΩ		+ -
		8kΩ	0.4kΩ			2.5mA
e x e r c i s e 3.26		For the circuit in Figure 3.129, write the node equations. Do

not solve, but write in matrix form: source terms on the left, unknown variables on the right.