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This question was asked previously many times...
i take no credit for this but i found this helpful
The shown figure is a quadrilateral (4 sides), so the sum of all its angles' measures is 360 degrees.
x+y = 80
So the sum of the other 2 angles' measures is 360 - 80, or 280.
Since the other 2 angles have equal measures (as stated in the problem), the measures must be 140.
DOING IT BY HAND:
Regular 3-sided shapes have 60 degree angles - 180 in total
Regular 4-sided shapes have 90 degree angles - 360 in total
Regular 5-sided shapes have ___ degree angles - 540 in total
Regular 6-sided shapes have ___ degree angles - 720 in total
Regular 7-sided shapes have ___ degree angles - 900 in total
Regular 8-sided shapes have ___ degree angles - 1080 in total
Regular 9-sided shapes have ___ degree angles - 1260 in total
140 is the total divided by the number of sides (1260/9), so the answer is 9 sides
You keep adding 180 as the total number of sides increases by 1
DOING IT BY EQUATION:
sum of all angles' measures =180(n-2), where n = number of sides
180(3-2)=180
180(4-2)=360
180(5-2)=540
180(6-2)=720
180(7-2)=900
180(8-2)=1080
180(9-2)=1260
9 angles of 140 degrees each = 1260
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