Which one of the following number (s) is/are rational?

Which one of the following number (s) is/are rational?

  1. A

    sin15

  2. B

    cos15

  3. C

    sin15cos15

  4. D

    sin15cos75

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    Solution:

    we have,

    sin15=sin(4530)=3122

     sin15=14(62) which is an irrational number

         cos15=cos(4530)=3+122

     cos15=14(6+2) which is an irrational number

           sin15cos15=12sin30=14which is a rational number

          sin15cos75=sin215=12(1cos30)=234 which is an irrational number

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