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Find the Value of Each Angle of an Octagon If Four of Its Angles Are Equal and the Other Four Are Each Greater than These by 20°. - Mathematics

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Question

Find the value of each angle of an octagon if four of its angles are equal and the other four are each greater than these by 20°.

Sum

Solution

An octagon has 8 sides, hence eight angles.
Sum of interior angles
= (n - 2) x 180°
= (8 - 2) x 180°
= 6 x 180°
= 1080°
Given four of its angles are equal.
Let each of the equal angles be x°
∴ Other four angles are = (x + 20)°
∴ x° + x° + x° + x° + (x + 20)° + (x + 20)° + (x + 20)° + (x + 20)° = 1080°
⇒ 8x° + 80° = 1080
⇒ 8x° = 1000°
∴ x° = 125°
∴ The four equal angles are 125°
The other four angles are 
= 125° + 20°
= 145°.

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Names of Polygons
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Chapter 18: Rectilinear Figures - Exercise 18.1

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Frank Mathematics [English] Class 9 ICSE
Chapter 18 Rectilinear Figures
Exercise 18.1 | Q 28
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