We know that, the sum of all angles of a polygon can be calculated by:

But in case of regular polygon, all the angles are equal. So, the measure of each angle can be found by dividing it by number of sides i.e n.
So, Value of each angle:

Given
- No. of sides of the regular polygon = 9
By using formula,
Measure of each interior angle:




So, measure of each angle = 140°
And we are done !!
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