Answer:
[tex]\Delta V=\Delta V_1+\Delta V_2+\Delta V_3[/tex]
Explanation:
We are given that three resistors R1, R2 and R3 are connected in series.
Let
Potential difference across [tex]R_1=\Delta V_1[/tex]
Potential difference across [tex]R_2=\Delta V_2[/tex]
Potential difference across [tex]R_3=\Delta V_3[/tex]
We know that in series  combination
Potential difference ,[tex]V=V_1+V_2+V_3[/tex]
Using the formula
[tex]\Delta V=\Delta V_1+\Delta V_2+\Delta V_3[/tex]
Hence, this is required expression for potential difference.