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Question

If the difference between the interior and exterior angles of a polygon is $36^\circ$, then find the number of sides in the polygon.

This question was previously asked in
RRB NTPC 2019 CBT 1 Question Paper (8-Mar-2021) (Shift 2)
The correct answer is
5

Polygon Angle Difference Calculation

To find the number of sides ($n$) of a polygon, we use the formulas for its interior and exterior angles.

  • Interior Angle ($I$): $I = \frac{(n-2) \times 180^\circ}{n}$
  • Exterior Angle ($E$): $E = \frac{360^\circ}{n}$

We are given that the difference between the interior and exterior angles is $36^\circ$.

Given: $I - E = 36^\circ$

Step-by-Step Calculation

  1. Substitute the formulas for $I$ and $E$ into the given equation:

    $ \frac{(n-2) \times 180^\circ}{n} - \frac{360^\circ}{n} = 36^\circ $

  2. Simplify the left side of the equation. Since the denominators are the same, combine the numerators:

    $ \frac{(n-2) \times 180^\circ - 360^\circ}{n} = 36^\circ $

  3. Expand the term in the numerator:

    $ \frac{180^\circ n - 360^\circ - 360^\circ}{n} = 36^\circ $

  4. Combine the constant terms in the numerator:

    $ \frac{180^\circ n - 720^\circ}{n} = 36^\circ $

  5. Multiply both sides by $n$ to eliminate the denominator:

    $ 180^\circ n - 720^\circ = 36^\circ n $

  6. Rearrange the equation to group terms with $n$:

    $ 180^\circ n - 36^\circ n = 720^\circ $

  7. Combine the terms with $n$:

    $ 144^\circ n = 720^\circ $

  8. Solve for $n$ by dividing both sides by $144^\circ$:

    $ n = \frac{720^\circ}{144^\circ} $

    $ n = 5 $

Therefore, the polygon has 5 sides.

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Similar Questions

  1. If the sum of the interior angles of a regular polygon is equal to four times the sum of its exterior angles, then what is the number of diagonals in the polygon?
  2. Find the ratio of the measure of an angle of a regular pentagon to that of a regular octagon.
  3. The area of an isosceles right angle triangle is $81 \text{ cm}^2$ . Find the length of its hypotenuse.
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Important Questions from Geometry

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