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Mathematics 7 Online
OpenStudy (anonymous):

@satellite73

OpenStudy (anonymous):

you rang?

OpenStudy (anonymous):

OpenStudy (anonymous):

ring ring

OpenStudy (anonymous):

the answer is 36, 36 but how?

OpenStudy (anonymous):

72? ok

OpenStudy (agent0smith):

^that can't be right @satellite73

OpenStudy (anonymous):

that is wrong, scratch that!

OpenStudy (agent0smith):

exterior angle?

OpenStudy (anonymous):

@agent0smith has it, i am way off base

OpenStudy (anonymous):

internal angles are 108 half of that is 54 i can't draw a damned picture, but you have a right triangle with one angle 54, right angle 90. remaining angle has to be whatever adds up to 180, namely 36

OpenStudy (anonymous):

hard without draw tool and latex

OpenStudy (anonymous):

maybe @agent0smith has a better explanation, or a picture

OpenStudy (agent0smith):

You can use the isosceles triangles with the 108 degree angles to find x... but yeah.. hard to explain w/o a pic.

jimthompson5910 (jim_thompson5910):

ABCDE is a regular pentagon (given), so each interior angle is I = 180(n-2)/n I = 180(5-2)/5 I = 108 That means angle EAB = 108 degrees. Similarly, angle EDC = 108 degrees (all 5 interior angles of this pentagon are 108 degrees) ------------------------ Triangle EAB is an isosceles triangle because AB = AE. Regular polygons have all sides congruent. Since the legs are congruent, the base angles are congruent. So we know that angle AEB = angle ABE They are both x degrees at the moment. The three angles add to 180 degrees x + x + 108 = 180 2x + 108 = 180 2x = 180 - 108 2x = 72 x = 72/2 x = 36 So, angle AEB = 36 degrees --------------------------- These similar steps can be used to show that angle CED = 36 degrees --------------------------- Now use the angle addition postulate to get angle AEB + angle BEC + angle CED = angle AED 36 + y + 36 = 108 y + 72 = 108 y = 108 - 72 y = 36

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