If α = 3 sin - 1 ⁡ 6 11   a n d   β = 3 cos - 1 ⁡ 4 9 , where the inverse…

If α=3sin-1611 and β=3cos-149, where the inverse trigonometric functions take only the principal values, then the correct options(s) is(are)
  1. cosβ>0
  2. sinβ<0
  3. cosα+β>0
  4. cosα<0

Solution

α=3sin-1611
Since π4>sin-1611>π6
3π4>3sin-1611>π2
cosα<0
cos3cos-149=4×493-3×49
=4×64729-129
=256-12×8172<0
5π12>cos-149>π3
5π4>3cos-149>π
sin3cos-149<0
3π4>3sin-1611>π2
5π4>3cos-149>π
2π>3sin-1611+3cos-149>3π2
cos3sin-1611+3cos-149>0

Asked in: JEE Advanced 2015 (Paper 2)

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