Question

Please try to tell how this happens angle OBA = 90-(theta/2)

Answer 1

Here angle of linaer line is 180'
so angle(TBV+XBF+OBA)=180'
then, 90'+(theta÷2)+x=180'=) theta÷2+X=180-90
angleOBA=90-theta÷2

Answer 2

Hey there !

Thanks for the question !

Answer:

Consider the ray AF.

Now it is a straight line. So, the angle made by a straight line is 180°.

So we can say that,

∠ OBA + ∠ OBX + ∠ XBF = 180°

Given that, ∠ OBX = 90° ; ∠ XBF = ( Ф / 2 )°

So Substituting them in the equation 1, we get,

∠ OBA + 90° + ( Ф / 2 )° = 180°

=> ∠ OBA = 180° - 90° - ( Ф / 2 )°

=> ∠ OBA = 90° - ( Ф / 2 )°

Hence we arrive at the solution that, ∠ OBA = 90 - ( Ф / 2 )°.

Hope my answer helped !