Nice video but I have to mention you made alot of mistakes when inserting your value into the y-bus matrix's. E.g y12 has already been given a value of -j3 according to d bus network u drew then y21 should be equal to -y12 i.e y21 = -y12 then d value of y21 shld be y21 = -(-j3) = j3 not -j3 . Then inserting this into the y-bus matrix since d off-diagonals have been assigned a -ve value thus d col of -y21 shld be -(j3) which equals -j3. Please sir/ma review your video