The problem is that a space heater develops a short circuit when to much current enters the circuit. The power supplied is 1500 W and the max current before short circuit is 15A. Firstly we have to calculate the resistance of the heater where I used P = I^2 R. But now we have to find the max reistance of the short circuit using circuit analysis, which we know R of the heater from before but we don't know the total current supplied. I read somewhere that the resistance of a short circuit is zero, but I may have read this wrong. Then we have to find the mimimum diameter of the wire(the short circuit) if it s 3mm long. It also givees a temp os 273K, and at this temp the heater wasn't working. Now I know you can set the derivative equal to zero to find max/min values. The other attempt I tried was to use alpha E = I/A, but after some algebra I get and area on both sides in the denominator, and they cancel, and I'm left with V/R = I.