If the TCR of each of the resistors is the same, then when you connect the resistors in series the TCR of the combination will be the same as any resistor individually. You can visualize this by imagining the 100k resistor to be made up of 50 identical 2k resistors in series (divide the 100k track into 50 equal segments). Since the TCR is a property of the track width and not of the track length, then any length of track will have the same TCR including a length of 102k made from 51 equal segments.

If the TCR of each of the resistors is different, then the situation is more complicated and you will have to use the formulas given in the link you referenced. If you do not understand the math then try to find someone who does. Sometime mathematics and formulas are the only answer to certain questions. (I'm sorry but I do not have time to go into it here as it is well after midnight for me, but maybe someone else can assist.)