In Fig.10.15, AOB is the diameter of the circle and C, D, and E are any three points on the semi-circle. Find the value of ACD + BED.
Join AE
ACDE is a cyclic quadrilateral and the sum of opposite angles in a cyclic quadrilateral is 180°
ACD + AED = 180° … (i)
Now, we know that the angle in a semi-circle is 90°
So, AEB = 90° … (ii)
By adding equation (i) & (ii), we get.
ACD + AED + AEB = 180° + 90°
ACD + BED = 270°
Hence the value of ACD + BED is 270°