Answer:
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<u>TRIGONOMETRY IDENTITIES TO BE USED IN THE QUESTION :-</u>
For any right angled triangle with one angle α ,
or 
or 
<u>SOME GENERAL TRIGNOMETRIC FORMULAS :-</u>
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or 
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or 
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Now , lets come to the question.
In a right angled triangle , let one angle be α (in place of theta) .
So , lets solve L.H.S.



= R.H.S.
∴ L.H.S. = R.H.S. (Proved)
All triangles must have angles that add up to the same amount of degrees, so if the two triangles share one exact point, it is assumed that those angles would be the same. Basically just use the fact that the sides are the same and marked by dashes, and the missing line can be proven with the use of the angles that are in between the point that both share.
It would be the last one because 5 columns are shaded and there are 10 columns all together. 50/100= 0.5