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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. The adjacent sides of a parallelogram are $4a$ and $3a$. If the angle between them is $60^{\circ}$, then one of the diagonals of the parallelogram will be:
  2. Every interior angle of a regular octagon is $135^\circ$. Find the exterior angle of the octagon.
  3. PQ is a diameter of circle whose centre is O. If a point R lies on a circle and $\angle RPO$ is $42^\circ$, then find $\angle RQP$.
  4. ABC is an equilateral triangle and O is its circumcentre. If the side of triangle is 6 cm, then the $\angle BOC$ is:
  5. If every interior angle of a regular polygon is $144^\circ$, then the polygon has ______ sides.
  6. The ratio of the numbers of sides of two regular polygons is $1 : 2$. If each interior angle of the first polygon is $140^\circ$, then the measure of each interior angle of the second polygon is:
  7. 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?
  8. Find the ratio of the measure of an angle of a regular pentagon to that of a regular octagon.
  9. What is the measure of each exterior angle of a regular octagon?
  10. The difference between the interior and exterior angles at a vertex of a regular polygon is $140^\circ$. The number of sides of the polygon is:

Important Questions from Geometry

  1. ABCDEF is a regular hexagon. Side of the hexagon is 36 cm. What is the area of the triangle AOB ?

  2. If ∆ABC ~ ∆DEF, and BC = 4 cm, EF = 5 cm and the area of triangle ABC = 80 cm 2, then the area of the triangle DEF is:

  3. If Δ ABC is right angled at B, AB = 12 cm and ∠CAB = 60°, determine the length of BC.  

  4. If ΔABC and ΔDEF are congruent triangles, then which of the following is FALSE?

  5. D and E are points on the sides AB and AC, respectively, of ΔABC such that DE is parallel to BC and AD ∶ DB = 7 ∶ 9. If CD and BE intersect each other at F. then find the ratio of areas of ΔDEF and ΔCBF.

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