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Would the final boolean expression to the circuit be right? Or do I have to multiply the brackets b(c*d)' out to bc' + bd'

schematic

simulate this circuit – Schematic created using CircuitLab

Edit: My new idea would be:

(a'+b)*(bc'+bd') = a'bc'+a'bd'+bbc' + bbd' = a'bc' + a'bd' + bc' + bd'

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  • \$\begingroup\$ Does + really mean "NOR?" \$\endgroup\$
    – JRE
    Commented May 4, 2019 at 19:48
  • \$\begingroup\$ Oh, sorry, I will edit sth. in the picture. \$\endgroup\$ Commented May 4, 2019 at 19:53
  • \$\begingroup\$ Now, there should be the right gate. \$\endgroup\$ Commented May 4, 2019 at 19:54
  • \$\begingroup\$ Is the expression to the circuit now right? \$\endgroup\$ Commented May 4, 2019 at 20:12
  • \$\begingroup\$ How do you get bc' + bd' out of b(c*d)'? For that fact, how do you figure to get that b out of (a'+b)? Wouldn't you have to do something with the a'? \$\endgroup\$
    – JRE
    Commented May 4, 2019 at 20:36

1 Answer 1

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Using De Morgan's theorem: (A*B)' = A' + B'

The output of AND3 gate in the image should be (a'+b)*(b*(c'+d')) instead of (a'+b)*(b*(c'*d'))

Which is how I assume you arrived at the edit part of your question. Now expanding the above expression, you get:

a'bc' + a'bd' + bc' + bd'

The above expression can be further simplified by grouping the terms:

bc'(a'+1) + bd'(a'+1)

And further using the Annulment law of Boolean Algebra, you get:

b (c' + d') as your final simplified expression.

Please let me know if this answered your question.

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  • \$\begingroup\$ Can I also do this ?: (a'+b)*(bc' + bd') = a'bc' + a'bd' + bbc' + bbd' (using here the idempotence law) = a'bc' + a'bd' + bc' + bd' (using here again the idempotence law) = bc' + bd' + bc' + bd' (using again the idempotence law) = bc' + bd' = b ( c'+d') ? \$\endgroup\$ Commented May 5, 2019 at 8:01
  • \$\begingroup\$ The first step is applying distributive law not idempotent law. And the second time your simplification idempotence law isn't right. a'bc' + a'bd' + bc' + bd' cannot become bc' + bd' + bc' + bd' (don't understand how a' terms were directly removed). The only way from the second step I see is to use the simplification I captured in the answer. \$\endgroup\$ Commented May 5, 2019 at 8:08
  • \$\begingroup\$ a'bc' + a'bd' + bc' + bd' cannot become bc' + bd' + bc' + bd' (don't understand how a' terms were directly removed).: a' + a' = a', thought i could do it as well with a' + a' = 0 \$\endgroup\$ Commented May 5, 2019 at 8:28
  • \$\begingroup\$ but it seems to be there is no other way than using the annulment law in the last step, i did not know this law before \$\endgroup\$ Commented May 5, 2019 at 8:29
  • \$\begingroup\$ @lightsodium a' + a' = a' not 0. Also you can't apply idempotent law directly because there are bc'/bd' terms associated with a'. An easy way to determine if any simplification is correct is to apply a set of values and check if the simplified and original expressions yield the same answer. Try a=1 b=1 c=d=0 in your case and it does not yield the same final logic state. \$\endgroup\$ Commented May 5, 2019 at 8:33

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