Answer:
BCDE= 100+ 80+100+80 = 360 degree
BAC = 20 degree
DBC = 100 degree
BDE = 80 degree
Shows all is correct
We associate isosceles trapezoid in this question, this helps us prove with angle A in the triangle vertices how we can find one of the adjacent angles from the trapezoid by subtraction when all angles within one single trapezoid = 360 degrees. We can use 20 degree angle A to subtract and find each alternative angle easier.
Step-by-step explanation:
The semi circle shows 9 stones
Where angles are interior to the trapezoid
Where all 4 sided shapes add up to 360 degree
We draw a line of symmetry on BCED angle
To make midway points BC and DE = 90 degree
The two new formed shapes are still 4 sided and add up to 360 degree.
BC + DE = 180 degree
BDE = Triangle 180 -20/2 = 160/2 = 80
BCDE = Trapezoid = 360
Trapezoid angle DBC = 360-80-80/2 = 360-160/2 = 200/2 = 100 degree
Finding interior angle A (BAC)
BAC = 180/9 = 20 degree
BAC * (2) = 360 degree circle
BAC = 360/18 = 20 degree
Proves BAC = 20 degree
20 degree is used in BAC workings above in bold and proves all trapezoid angles are correct. We now know this is an isosceles trapezoid and that is why symmetry and midway points can help us find the angles without any given length.
