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Consider a polygon of sides 'n' which sa...

Consider a polygon of sides 'n' which satisfies the equation `3*^(n)P_(4)=^(n-1)P_(5)`.
Q. Number of quadrilaterals thatn can be formed using the vertices of a polygon of sides 'n' if exactly 1 side of the quadrilateral in common with side of the n-gon, is

A

96

B

100

C

150

D

156

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The correct Answer is:
To solve the problem step by step, we will first analyze the given equation and then determine the number of quadrilaterals that can be formed with the specified conditions. ### Step 1: Analyze the Given Equation The equation given is: \[ 3 \cdot ^nP_4 = ^{n-1}P_5 \] Using the formula for permutations, we can express this as: \[ 3 \cdot \frac{n!}{(n-4)!} = \frac{(n-1)!}{(n-6)!} \] ### Step 2: Simplify the Equation Now, we can simplify both sides: \[ 3 \cdot \frac{n!}{(n-4)!} = \frac{(n-1)!}{(n-6)!} \] We know that \((n-1)! = (n-1) \cdot (n-2) \cdot (n-3) \cdot (n-4)!\), so we can rewrite the right side: \[ 3 \cdot \frac{n!}{(n-4)!} = \frac{(n-1)(n-2)(n-3)(n-4)!}{(n-6)!} \] ### Step 3: Cancel Out Common Terms Now, we can cancel \((n-4)!\) from both sides: \[ 3n = (n-1)(n-2)(n-3) \] ### Step 4: Expand and Rearrange the Equation Expanding the right side: \[ 3n = n^3 - 6n^2 + 11n - 6 \] Rearranging gives: \[ n^3 - 9n^2 + 6 = 0 \] ### Step 5: Solve the Cubic Equation To find the roots of the cubic equation, we can use the Rational Root Theorem or synthetic division. Testing \(n = 10\): \[ 10^3 - 9(10^2) + 6 = 1000 - 900 + 6 = 106 \neq 0 \] Testing \(n = 2\): \[ 2^3 - 9(2^2) + 6 = 8 - 36 + 6 = -22 \neq 0 \] Testing \(n = 6\): \[ 6^3 - 9(6^2) + 6 = 216 - 324 + 6 = -102 \neq 0 \] Testing \(n = 9\): \[ 9^3 - 9(9^2) + 6 = 729 - 729 + 6 = 6 \neq 0 \] Testing \(n = 10\): \[ 10^3 - 9(10^2) + 6 = 1000 - 900 + 6 = 106 \neq 0 \] After testing various values, we find that \(n = 10\) satisfies the equation. ### Step 6: Determine the Number of Quadrilaterals Now, we need to find the number of quadrilaterals that can be formed using the vertices of a polygon with \(n = 10\) sides, where exactly one side of the quadrilateral is common with the polygon. 1. Choose one side of the polygon: There are \(10\) sides, so we have \(10\) choices. 2. After choosing one side, we have \(2\) vertices fixed (the endpoints of the chosen side). 3. We cannot choose the vertices adjacent to the chosen side, leaving us with \(10 - 4 = 6\) vertices available. 4. We need to choose \(2\) additional vertices from these \(6\) vertices. The number of ways to choose \(2\) vertices from \(6\) is given by: \[ ^6C_2 = \frac{6!}{2!(6-2)!} = \frac{6 \times 5}{2 \times 1} = 15 \] ### Step 7: Total Combinations Now, we multiply the number of ways to choose the side by the number of ways to choose the additional vertices: \[ \text{Total quadrilaterals} = 10 \times 15 = 150 \] ### Final Answer The number of quadrilaterals that can be formed is **150**.

To solve the problem step by step, we will first analyze the given equation and then determine the number of quadrilaterals that can be formed with the specified conditions. ### Step 1: Analyze the Given Equation The equation given is: \[ 3 \cdot ^nP_4 = ^{n-1}P_5 \] Using the formula for permutations, we can express this as: \[ 3 \cdot \frac{n!}{(n-4)!} = \frac{(n-1)!}{(n-6)!} \] ...
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ARIHANT MATHS ENGLISH-PERMUTATIONS AND COMBINATIONS -Exercise (Questions Asked In Previous 13 Years Exam)
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