Q.Convert $Y = (A + \overline{B})(B + C)$ into canonical POS form

A canonical (standard) POS form must have every sum (OR) term containing all three variables. Each OR term is expanded by ORing it with the AND of any missing variable and its complement. …

[!TLDR]

Fill in the missing variable in each OR term of $Y = (A + \overline{B})(B + C)$ so every sum term holds all of A, B and C, giving the four-maxterm canonical POS.

In a canonical (standard) POS expression each OR term must contain every input variable. Using $X\overline{X} = 0$, each sum term is ORed with $X\overline{X}$ for its missing variable and then distributed by $P + QR = (P + Q)(P + R)$.

Term $(A + \overline{B})$: variable C is missing, so OR with $C\overline{C}$:

Term $(B + C)$: variable A is missing, so OR with $A\overline{A}$:

$(B + C) + A\overline{A} = (A + B + C)(\overline{A} + B + C)$ …