The thermal energy developed in a current carrying resistor is given by U= i(sq)RT and also U= vit. should we say that U is prpoportional to i(sq) or i ?

sq= square

in general e=vit,but in a resistor v is directly proportional to i, with a constant of proportionality that varies from resistor to resistor and v=ir, therefore e= i²rt for resistors only and is equal to vit otherwise