Question:
If cos (sin-1 2/5 + cos-1 x) = 0, then x is equal to
(a) 1/5
(b) 2/5
(c) 0
(d) 1
Solution:
(b) 2/5
Given,
cos (sin-1 2/5 + cos-1 x) = 0
So, this can be rewritten as
sin-1 2/5 + cos-1 x = cos-1 0
sin-1 2/5 + cos-1 x = π/2
cos-1 x = π/2 – sin-1 2/5
cos-1 x = cos-1 2/5 [Since, cos-1 x + sin-1 x = π/2]
Hence,
x = 2/5
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