Question

Hello, I'm having problems with the first exercise here https://www.dropbox.com/s/jas9x6mjsusihi4/Ex_All_groups_v3.pdf

How do I calculate the Thevenin voltage there?

Thanks!

Answer 1

To solve the problem you must use the principle of superposition, short out all independent voltage sources and open all independent current sources except the one under consideration. Then add the resultant VB from each source, this is the Thevenin voltage. I'll do this for the left 5 v source to get you started
VA = 5[(10+10||20)||5/{2 + (10+10||20)||5}]
VB = VA[20||10/{10+20||10}]
|| means parallel 10||20=20/3
Do the same for all sources and then add the VBs

Answer 2

Notice VB is factorable
VA[20||10/{10+20||10}] = VA[2||1/{1+2||1}]
1||a = a/(1+a)
VA is somewhat factorable
5[(10+10||20)||5/{2 + (10+10||20)||5}] =
5[((10(1+1||2))||5/{2 + (10(1+1||2))||5}]