A Detailed Tutorial on Polygons and Angles

Polygons

A polygon is any closed figure which is bounded by at last three straight lines. It implies that a polygon can have more than three sides, a polygon is named according to the number of sides it has thus.

Number of SidesName of Polygon
3Triangle
4Quadrilateral
5Pentagon
6Hexagon
7Heptagon
8Octagon
9Nonagon
10Decagon
  

Types of Polygon:

Polygon can also be classified into the following ways

  • Convex Polygon: In this type of Polygon, each interior angle is less than 180o
  • Reentrant Polygon: This is a polygon with one or more of the interior angles reflex i.e greater than 180o
  • Equivalent Polygon: All its sides are equal
  • Equiangular polygon: All its angles are equal
  • Regular Polygons: That is polygon in which all its sides is an angle are equal

Problems involving polygon ha to do with theorems. So we are going to walk with two theorems in order to tackle problems on it

Theorem 1:

The sum of the interior angle of any n-sided (Covex)

Polygon is given as (2n-1) right angle

i.e (2n – 4) 9-

that means

interior angles of a polygon is given by(2n-4)90o

note the formula

The second says that the sum exterior angles of any convex polygon is for right angles.

i.e sum of exterior angles of a polygon = 4 right angles

= 4 x 90 = 360

Therefore, Sum of angle of any Polygon is 360

N/B: n is the number of sides of any polygon.

This this information we have obtain, we can now get into solving some problems on this topic.

Example 1:

The sum of the angles of a regular polygon is 2520, how many sides does the polygon

Solution

Sum of interior angle of regular polygon = (2n-4)90o

Since the sum of the angles of a regular polygon is 2520

(2n-4)90o= 2520o

Let open the bracket

2n x 9 – 4 x 9 = 2520o

180on = 360o = 2520

Collect like terms

180n = 2520o + 360o

180n/180 = 2880/180

N = 16

Therefore, the number of sides of the polygon is 16

Example 2:

One angle of an octagon is 65o.The other are equal to each other find them

Solution

An octagon as 8 sides let each of the remaining 7 angles be x

Again, sum of interior angles of a regular polygon = (2n-4)90o

And one of the angles is 65o

This means

7 xx + 65o = (2n-4)90o

7x + 65o = (2 x 8 – 4) 90o

Let solve the right hand side first

(16-4)90o

= 12 x 90o = 1080o

Then, 7x + 65o = 1080

Collect like terms

7x = 1080o = 650o

7x/7 = 1015/7

X = 145o

Therefore, the values of the other 7 remaining angles is 145o

Example 3:each angle of regular polygon is 165o how many sides hat it?

Solution
each extains angle

= 180o – 165o = 15o

Sum of angle of any polygon is 360o

Solve n = 3060o/exterior angle

N = 360/15 = 24

Therefore polygon has 24 sides

Example 4:

If the angle of a quadrilateral are xo x + 10, x +20 and x + 30o find the value of each angle

Solution

Quadrilateral is a polygon with 4 sides

i.e n = 4

again, sum of interior angle of a regular polygon 

= (2n-4)90o

That means

Sum of interior angle of a quadrilateral

=(2 x 4 – 4) x 90o

-(8-4) x 90o

– 4 x 90o = 360

Add the angles given and equate it 3600o

x + x + 12 + x + 20o x + 30o  = 360o

collect like terms

4x + 60 – 60

4x = 360 – 60

4x/4 = 300/4

X = 75o

Therefore each of the angle will be 75, 75 + 10, 75 + 2, 75 + 30

75, 85, 95, and 105

Read Also:

Example 5:

Each interior of a regular polygon is 120o more than each of the exterior angles. How many sides nets it?

Solution

Sum of interior angles of a regular polygon =(2n-4)90o

Again,  Each exterior

Angle = 180 – 120 = 60

120 makes then each of the exterior angles 280 – 120 = 60

120  + Each exterior angle = 180 – 120 = 60o

120 more than each of the exterior means 120 + each exterior angle means

120 + each exterior

= 120 + 60 = 180

Therefore,

(2n-4) 90o = 180

180n – 360 = 180

180n = 180 + 360

180n/180 = 540/180

N = 3

Therefore, the number of sides = 3

Example 6:

The angle of the hexagon are y, (y+15), (y+25) (y+ 35)o

(y+45) an d(y + 54) find

Solution

Sum of angles of interior

Angles of a polygon = (2n-4)90o

Sum of angles of a hexagon = (2 x 6 – 4)90o

(12 – 4) 90o

8 x 90o 720o

N/B Hexagon is polygon with six sides

Add the angles and equate it to 720

Y+y+15+y+25+y+35+y

45+y+54=720

6y+174=721

6y = 720 – 174

6y/6 = 546/6

Y = TI

Therefore, the value of y is 91o

In conclusion, when faced with problems on polygon, always remember the theorems and the different formulas used. Make sure you write down these formulas for reference purpose.

With the problems we have solved today, I believe polygon problems cannot be a barrier to you.

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