Please answer my question

In ΔOAB, OA = r and $OD = \frac{r}{2}$ .

∠ODA = 90°

In ΔOAD,

$\sin ∠ OAD = \frac{OD}{OA} [∵ \sin θ = \frac{Perpendicular}{Hypotenuse}] ∴ \sin ∠ OAD = \frac{\frac{r}{2}}{r} \Rightarrow \sin ∠ OAD = \frac{1}{2} \Rightarrow \sin ∠ OAD = sin 30 ° [∵ \sin 30 ° = \frac{1}{2}] \Rightarrow ∠ OAD = 30° ∴ ∠ BAO = 30°$

The concepts of trigonometry are taught in grade X.

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