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Motion In A Plane

Question
CBSEENPH11018561

There are two angles of projection for which horizontal range is same. Prove that the sum of maximum heights for these two angles is independent of angle of projection.

Solution

Given, horizontal range is same for two angles of projection. 
The angles are θ and 90°–θ.
Maximum height H1 for angle projection θ is,
                     straight H subscript 1 equals fraction numerator straight u squared sin squared straight theta over denominator 2 straight g end fraction 
Maximum height H2 for angle projection 90°–θ is, 
          space space space space straight H subscript 2 equals fraction numerator straight u squared sin squared left parenthesis 90 degree minus straight theta right parenthesis over denominator 2 straight g end fraction equals fraction numerator straight u squared cos squared straight theta over denominator 2 straight g end fraction 

Now, sum of maximum height is,  
  space space space space space straight H subscript 1 plus straight H subscript 2 equals fraction numerator straight u squared sin squared straight theta over denominator 2 straight g end fraction plus fraction numerator straight u squared cos squared straight theta over denominator 2 straight g end fraction equals fraction numerator straight u squared over denominator 2 straight g end fraction   

Hence the result.