Mathematics - Permutation & Combination Question with Solution | TestHub

MathematicsPermutation & CombinationnPr & nCrMedium2 minPYQ_2015

MathematicsMediumsingle choice

If in a regular polygon the number of diagonals is $54$ , then the number of sides of this polygon is:

Options:

Answer:

Solution:

Number of diagonals of an $' n'$ sided polygon is

$^{n} C_{2}$ $- n = 54$

$\frac{n (n - 1)}{1.2} - n = 54$

$\frac{n^{2} - n}{2} - n = 54$

$n^{2} - 3 n = 108$

$n^{2} - 3 n - 108 = 0$

$(n - 12) (n + 9) = 0$

$n = 12$

Stream:JEESubject:MathematicsTopic:Permutation & CombinationSubtopic:nPr & nCr

⏱ 2mℹ️ Source: PYQ_2015

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