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Mathematics 19 Online
OpenStudy (word2):

Check my work

OpenStudy (word2):

Quadrilateral BCDE is inscribed inside a circle as shown below. Write a proof showing that angles C and E are supplementary.

OpenStudy (word2):

My work : The first thing i did was i drew a line from A to each of the vertex's. This resulted in four isosceles triangles. All four of the triangles have equal bases. The four isosceles triangle i labeled a,b,c,d. Quadrilateral BCDE = 360 2a + 2b + 2c + 2d = 360 a + b + c + d = 180 (a+d) + (b+c) = 180 Angles E and C measure 180 proving that they are supplementary

OpenStudy (word2):

@welshfella can you help me again?

OpenStudy (welshfella):

the first statment is wrong 2a + ... adds up to 720 degrees. the best way si as follows

OpenStudy (welshfella):

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OpenStudy (welshfella):

use the theorem The angle subtended by a chord at the center of circle = 2 * angle subtended on the circle So in the above diagram <EAC = 2 * EBC and reflex < EAC = 2 * <EDC

OpenStudy (word2):

i am comply lost so far

OpenStudy (welshfella):

And how many degrees are in <EAC + reflex < EAC?

OpenStudy (welshfella):

|dw:1470056173018:dw|

OpenStudy (word2):

would it be 180 degrees ?

OpenStudy (welshfella):

the angle at the center = 2 * angle EBC

OpenStudy (welshfella):

|dw:1470056244290:dw|

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