24. 如圖(十三)所示之JFET電路,VDD = 12 V,RG1 = 600 k Ω,RG2 = 120 k Ω,RD = 4.7 k Ω,RS=3 kΩ,若汲極電壓VD =6V,則G、S 兩端之電壓VGS約為何?