= A + B’C …….(1)
The first term A is missing two variables B and C, therefore
A = A (B + B’) = AB + AB’ = AB (C+C’) + AB’ (C+C’)
= ABC + ABC’ + AB’C + AB’C’ …….(2)
The second term B’C is missing variable A, therefore
B’C = B’C (A + A’)
= AB’C + A’B’C …….(3)
Now, Substitute (2) and (3) in (1) we get
ABC + ABC’ + AB’C + AB’C’ + AB’C + A’B’C.