Question 1169821
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Refer to the drawing that tutor mananth made. 
However, keep in mind that points B, C, and D should be on the same straight line.


AC = CD leads to angles CAD and ADC being congruent. They are denoted as y in the drawing. 
This similar line of logic also explains why angleABC = angleBCA = 2x.


From here we can use the remote interior angle theorem
angleCAD + angleADC = angleBCA
y+y = 2x
2y = 2x
y = x
x = y
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