यदि (^{n}P_r=n(n-1)\cdots(n-r+1)) है तो factorial रूप में सही अभिव्यक्ति कौन-सी है?
If (^{n}P_r=n(n-1)\cdots(n-r+1)) then which factorial form is correct?
Explanation opens after your attempt
Correct Answer
B. (^{n}P_r=\frac{n!}{(n-r)!})
Concept
After (r) decreasing factors the remaining tail is ((n-r)!). In exams put the missing tail in the denominator.
Why this answer is correct
The correct answer is B. (^{n}P_r=\frac{n!}{(n-r)!}). After (r) decreasing factors the remaining tail is ((n-r)!). In exams put the missing tail in the denominator.
Exam Tip
घटते हुए (r) गुणकों के बाद बचे ((n-r)!) से factorial पूरा होता है। परीक्षा में missing tail को denominator बनाएं।
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