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Ray BO is the bisector of ∠ CBE.
Therefore, ∠ CBO = 1/2 ∠ CBE
= 1/2 (180° – y)
= 90° – 2y/2 (1)
Similarly, ray CO is the bisector of ∠ BCD.
Therefore, ∠ BCO = 1/2∠ BCD
2 (180° – z)
= 90° – z/2 (2)
In ∆ BOC, ∠ BOC + ∠ BCO + ∠ CBO = 180° (3)
Substituting (1) and (2) in (3), you get
∠ BOC + 90° – z/2+90° –y/2=180°
So, ∠ BOC = z/2+y/2
or, ∠ BOC = 1/2(y + z) (4)
But, x + y + z = 180° (Angle sum property of a triangle)
Therefore, y + z = 180° – x
Therefore, (4) becomes
∠ BOC = 1/2 (180° – x)
= 90° – x/2
= 90° – 1/2∠ BAC
hence prooved
hope it helps
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