Computers rely upon strict interpretations of logical statements. Can you think like a computer, and identify the statement below that is false ?
Assume that b and c are variables which represent non-negative integers.
A) ¬ ∀ c : ∃ b : ( 2 b = c )
B) ∀ c : ∃ b : ¬ ( 2 b = c )
C) ¬ ∃ b : ∀ c ( 2 b = c )
D) ∀ c : ¬ ∃ b : ( 2 b = c )
These symbols have the following meanings:
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You also need to prove that A), B) and C) are true.
A) "Not all c , such that some of b satisfies 2 b = c " means some (or no) c and some b makes this true, which is true. ex. 2 ∗ ( 2 ) = ( 4 ) .
B) "All of c , such that some of b satisfies 2 b = c " means any b can make this equation false for any c , which is true. ex. 2 b = 5 for any integers b .
C) "None of b , such that all of c satisfies 2 b = c " means if c changes, b will not stay the same, which is true. (because f ( x ) = 2 b is a 1-by-1 function).
D) "All of c , such that none of b satisfies 2 b = c " means every number c can't be written in the form of 2 b , which is false, because even number can be written as 2 k , ∀ k ∈ Z + ∪ { 0 }.
Therefore, the answer is D .~~~
In the third point "C", i think it should be f ( b ) = 2 b where you say that f ( x ) = 2 b is a 1-by-1 function.
Oops, my bad. XD
Just click 'edit' on upper right corner and change it ;)
if c=2 then there exist b=1 such that 2b=c. hence d is false.
#include<iostream.h>
int main()
{
cout<<"All right, I am nuts. Sue me. Here's the solution, though -\n\n"<<endl;
cout<<"A)\nNot for all (i.e. For some) c, there exists some b";
cout<<" such that twice of b is c.\nThis is true.\n"<<endl;
cout<<"B)\nFor all c, there exists some b such that twice of b";
cout<<" is not c.\nThis is true.\n"<<endl;
cout<<"C)\nThere does not exist any b such that for all c,";
cout<<" twice of b comes out to be c.";
cout<<"\nOR\n";
cout<<"For any fixed value of b, \'2b = c\' is not true for ALL c.";
cout<<"\nThis is true\n"<<endl;
cout<<"D)\nFor all c, there does not exist any b such that twice of b is c.";
cout<<"\nOR\n";
cout<<"\'There exists some b such that twice of b is c.\' is false for all c.";
cout<<"\nThis is FALSE.\n\n"<<endl;
cout<<"So, answer (false) is D.";
return(0);
}
Ask for proof of any of these in the comments, if you want to ; )
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D logically says "For all c there does not exist a value of b such that 2 × b = c . " It is easy to prove this false by counterexample. If c = 4 , then a possible value for b is 2 , which contradicts the logic of the statement. Therefore, D is false.