My second formula is the same as yours.
The first one can be derived as
R1 = R0(1 + aT1) ...(i)
R2 = Ro (1 +aT2)... (ii)
Divide (i) by (ii)
And you'll get the 1st formula.
Both formulae are correct.
The difference in their usage is that When T1 is 0deg. The 1st formula changes to the...
When we are supposed to calculate the value of "temperature coefficient of resistance " i.e. α , how are we supposed to choose between the following two formulae :
α = (R2 - R1) / (R1*T2 - R2* T1 )
or
α = (R2 - R1)/ [ R1 *( T2-T1) ]
I have attached scanned pictures of two similar...