(D_n=n!\left(1-\frac{1}{1!}+\frac{1}{2!}-\cdots+(-1)^n\frac{1}{n!}\right)) किस principle से आता है?
The formula (D_n=n!\left(1-\frac{1}{1!}+\frac{1}{2!}-\cdots+(-1)^n\frac{1}{n!}\right)) comes from which principle?
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Correct Answer
A. Inclusion-exclusion
Concept
Permutations with fixed points are subtracted and added alternately. In exams think of inclusion-exclusion when no object is in its correct place.
Why this answer is correct
The correct answer is A. Inclusion-exclusion. Permutations with fixed points are subtracted and added alternately. In exams think of inclusion-exclusion when no object is in its correct place.
Exam Tip
Fixed points वाले permutations को alternating तरीके से घटाया और जोड़ा जाता है। परीक्षा में कोई object सही स्थान पर न हो तो inclusion-exclusion सोचें।
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