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See the attached figure:
To prove: angle A + angle B + angle C = 180°
Draw line through B parallel to AC and label two points D and E.
angle ABD + angle ABC + angle CBE = 180°- (1) (because DE is a straight line)
angle ABD = angle BAC (Alternate interior angles) - (2)
angle CBE = angle BCA (Alternate interior angles) - (3)
Substitute values for angle ABD and angle CBE in - (1)
angle BAC + angle ABC + angle BCA = 180
angle A + angle B + angle C = 180°
3 3 3
if it was useful please mark as best
thanks yes it is useful for me
But the figure doesn't have a parallel line....
it actually has, but when i put the image it appered to be like that
it is parallel
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