Trigonometrical Ratios and Identities 1 Question 11

11. Which of the following numbers is rational?

(1998,2M)

(a) sin15

(b) cos15

(c) sin15cos15

(d) sin15cos75

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Answer:

Correct Answer: 11. (b)

Solution:

  1. Since, sin15=1223 and cos15=122+3 and sin15cos75=sin15sin15=14(23)

Therefore, all these values are irrational and

sin15cos15=122sin15cos15=12sin30=14, which is rational. 



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