想问一个关于集成运放的题目,谢谢

设 电阻 R2、R3、R4 连接处的电位是 v',则有：
v0+ = 0 - v'/R4 * R5 = -10v'
i1 = vi/10 = i2 = -v'/20
所以,v' = -2vi.那么 v0+ = 20vi
另外,i2 = i3 + i4
i3 = i2 - i4 = -v'/R2 - v'/R4 = -v'/20 -v'/10 = -3v'/20
那么,v0- = v'- i3 * R3 = v' + 3v'/20 * 20 = 4v'= -8vi
因此,
v0 = v0+ - v0- = 20vi - (-8vi) = 28vi