Question

please tell 2nd question

Answer 1

In triangle DOE,
OD = AB/2 (Since, it is the radius)
DE = AB/2 (Given)
Therefore, OD =DE
So, angle AEC = angle DOE(Since its an isosceles triangle)
=18 degrees
In triangle ODC
angle ODC = 2×angle AEC(Since exterior angle of triangle DOE = Sum of its opposite interior angles)
= 2 × 18 = 36 degrees
Since, OD = OC (as they are tge radii of the same circle)Therefore, angle ODC = angle OCD
angle DOC = 180 - 2 × angle ODC = 108 degrees
We know that,
angle DOE + angle DOC + angle COA = 180(Adjacent angles on the same line)
Therefore, angle COA = 180 - 18 - 108 = 54 degrees(ANSWER)