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Published on: 01/12/2018
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Questions + Answers key
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1.
Convert \(\bar { X } .Y+Y.(\bar { Z } (\bar { Z } +Y))\) into canonical product of sums form.
2.
Given the following truth table, device a Sum of Product(SOP) and Product of Sum(POS) form of boolean expression from it:
| A | B | C | F(A,B,C) |
| 0 | 0 | 0 | 1 |
| 0 | 0 | 1 | 1 |
| 0 | 1 | 0 | 1 |
| 0 | 1 | 1 | 1 |
| 1 | 0 | 0 | 0 |
| 1 | 0 | 1 | 1 |
| 1 | 1 | 0 | 1 |
| 1 | 1 | 1 | 0 |
3.
Convert the following boolean expression into the equivalent canonical Product of Sum(POS) form \(A.\bar { B } .C+\bar { A } .B.C+\bar { A } .B.\bar { C } \)
4.
Verify the following algebraically:\(\bar { X } .Y+X.\bar { Y } =(\bar { X } +\bar { Y } ).(X+Y)\)
5.
Verify the following using boolean laws:
\(A+C=A+\overset { - }{ A } .C+B.C\)
6.
How many input combinations can be there in the truth table of a logic system having(N) input binary variables?
7.
Write the dual of the boolean expression \((A+0).(A.1.\bar { A } )\)
8.
Write the Sum of Product(SOP) form of the function F(P,Q, R) for the following truth table representation of F:
| P | Q | R | F |
| 0 | 0 | 0 | 1 |
| 0 | 0 | 1 | 0 |
| 0 | 1 | 0 | 0 |
| 0 | 1 | 1 | 1 |
| 1 | 0 | 0 | 0 |
| 1 | 0 | 1 | 0 |
| 1 | 1 | 0 | 1 |
| 1 | 1 | 1 | 1 |
1.
Step 1 Simplify the given expression using appropriate theorems/rules.
\(\bar { X } .Y+Y.(\bar { Z } (\bar { Z } +Y))=\bar { X } .Y+Y.(\bar { Z } .\bar { Z } +\bar { Z } .Y)\quad \quad \quad \quad [By\quad using\quad Distributive\quad law]\\ =\bar { X } .Y+Y.(\bar { Z } +\bar { Z } .Y)\quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad [\because \quad \bar { Z } .\bar { Z } =\bar { Z } ]\\ =\bar { X } .Y+Y.\bar { Z } .(1+Y)\\ =\bar { X } .Y+Y.\bar { Z } .1\quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad [\because \quad 1+Y=1]\\ =\bar { X } .Y+Y.\bar { Z } \\ \\ \)
Step 2 To convert into POS form applying the boolean algebra rule
\(\bar { X } .Y+Y.\bar { Y } =(\bar { X } .Y+Y).(\bar { X } .Y+\bar { Z } )\\ \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad [\because \quad X+Y.Z=(X+Y).(X+Z)]\\ =(Y+\bar { X } .Y).(\bar { Z } +\bar { X } .Y)\quad \quad [\because X+Y=Y+X]\\ =(Y+\bar { X } ).(Y+Y).(\bar { Z } +\bar { X } ).(\bar { Z } +Y)\\ =(\bar { X } +Y).(Y).(\bar { X } +\bar { Z } ).(Y+\bar { Z } )\quad \quad [\because \quad Y+Y=Y)\)
Step 3 Wherever a variable is missing, ad that term with (missing variable. complement of missing variable)
\(=(\bar { X } +Y+Z.\bar { Z } ).(X.\bar { X } +Y+Z.\bar { Z } ).(\bar { X } +Y.\bar { Y } +\bar { Z } ).(X.\bar { X } +Y+\bar { Z } )\\ =(\bar { X } +Y+Z).(\bar { X } +Y+\bar { Z } ).(X.\bar { X } +Y+Z).(X.\bar { X } +Y+\bar { Z } ).(\bar { X } +Y+\bar { Z } ).(\bar { X } +\bar { Y } +\bar { Z } ).((X+Y+\bar { Z } ).(\bar { X } +Y+\bar { Z } )\\ =(\bar { X } +Y+Z).(\bar { X } +Y+\bar { Z } ).(X+Y+Z).(\bar { X } +Y+Z).(X+Y+\bar { Z } ).(\bar { X } +Y+\bar { Z } ).(\bar { X } +Y+\bar { Z } ).(\bar { X } +\bar { Y } +\bar { Z } ).((X+Y+\bar { Z } ).(\bar { X } +Y+\bar { Z } )\\ \)
Step 4 Remove all duplicate terms, i.e.,
\(=(\bar { X } +Y+Z).(\bar { X } +Y+\bar { Z } ).(X+Y+Z).(X+Y+\bar { Z } ).(\bar { X } +\bar { Y } +\bar { Z } )\\ \)
This is the desired canonical Product of Sums form.
2.
| A | B | C | F | MInterms | Maxterm |
| 0 | 0 | 0 | 1 | \(\bar { A } .\bar { B } .\bar { C } \) | |
| 0 | 0 | 1 | 1 | \(\bar { A } .\bar { B } .C\) | |
| 0 | 1 | 0 | 0 | \(A+\bar { B } +C\) | |
| 0 | 1 | 1 | 1 | \(\bar { A } .B.C\) |
| A | B | C | F | Minterms | Maxterm |
| 1 | 0 | 0 | 0 | \(\bar { A } +B+C\) | |
| 1 | 0 | 1 | 1 | \(A.\bar { B } .C\) | |
| 1 | 1 | 0 | 1 | \(A.B.\bar { C } \) | |
| 1 | 1 | 1 | 0 | \(\bar { A } +\bar { B } +\bar { C } \) |
Sum of Products(SOP) expression contain sum of all minterms for output as 1.
\(=\bar { A } .\bar { B } .\bar { C } +\bar { A } .\bar { B } .C+\bar { A } .B.C+A.\bar { B } .C+A.B.\bar { C } \)
\(=\sum (0,1,3,5,6)\)
Product of Sum(POS) expression contains product of all maxterms for output as 0.
\(=(A+\bar { B } +C).(\bar { A } +B+C).(\bar { A } +\bar { B } +\bar { C } )\quad \)
\(=\prod (2,4,7)\)
3.
F= \(A.\bar { B } .C+\bar { A } .B.C+\bar { A } .B.\bar { C } \)
i.e., (101)+(011)+(010)=m5+m3+m2=\(\sum (2,3,5)\)
POS expression will be :
\(=\prod (0,1,4,6,7)\)
= M0.M1.M4.M6.M7
=(000).(001).(100).(110).(111)
=\((A+B+C).(A+B+\bar { C } ).(\bar { A } +B+C).(\bar { A } +\bar { B } +C).(\bar { A } +\bar { B } +\bar { C } )\)
4.
\(\bar { X } .Y+X.\bar { Y } =(\bar { X } +\bar { Y } ).(X+Y)\)
Taking R.H.S \((\bar { X } +\bar { Y } ).(X+Y)\)
\(=\bar { X } .X+\bar { X } .Y+\bar { Y } .X+\bar { Y } .Y\)
\(=0+\bar { X } .Y+\bar { Y } .X+0\quad \quad \quad \quad \quad \quad [\therefore \quad X.\bar { X } =0]\)
\(=\bar { X } .Y+\bar { Y } .X\) \([\bar { X } .Y=\bar { Y } .X]\)
= L.H.S Hence proved.
5.
\(A+C=A+\overset { - }{ A } .C+B.C\)
RHS=\(A+\overset { - }{ A } .C+B.C\)
\(A+C=A+\overset { - }{ A } .C+B.C\\ \quad \quad \quad \quad =(A.\overset { - }{ A } ).(A+C)+B.C\\ \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad [By\quad using\quad distributive\quad law]\\ \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad [By\quad using\quad A+\overset { - }{ A } =1]\\ \quad \quad \quad \quad =1.(A+C)+B.C\\ \quad \quad \quad \quad =A+C+B.C=A+C.(1+B)\\ \quad \quad \quad \quad =A+C.(1)=A+C\quad \quad \quad \quad \quad \quad \quad \quad \quad \quad [\therefore 1+B=1]\\ \quad \quad \quad \quad =LHS\)
6.
( )
2N input combinations can be there in the truth table of a logic system.
7.
( )
Using duality principle, changing (+) to (.) and vice-versa and by replacing 0's with 1's and 1's with 0's, the dual for the given expression is as follows:\((A.1)+(A+0+\bar { A } )\)
8.
( )
| P | Q | R | F | Minterms |
| 0 | 0 | 0 | 1 | \(\bar { P } .\bar { Q } .\bar { R } \) |
| 0 | 0 | 1 | 0 | \(\bar { P } .\bar { Q } .R \) |
| 0 | 1 | 0 | 0 | \(\bar { P } .Q .\bar { R } \) |
| 0 | 1 | 1 | 1 | \(\bar { P } . Q .R \) |
| 1 | 0 | 0 | 0 | \(P .\bar { Q } .\bar { R } \) |
| 1 | 0 | 1 | 0 | \(P .\bar { Q } .R \) |
| 1 | 1 | 0 | 1 | \(P.Q .\bar { R } \) |
| 1 | 1 | 1 | 1 | P.Q.R |
SOP form of function F(P, Q, R) is: \(=\bar { P } .\bar { Q } .\bar { R } +\bar { P } .Q.R+P.Q.\bar { R } +P.Q.R\)
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