1.

If `"log"_("cos"x) "tan" x + "log"_("sin"x) "cot" x =0,` then x =A. `n pi + (pi)/(4), n in Z`B. `2n pi + (pi)/(4), n in Z`C. `2n pi -(3pi)/(4), n in Z`D. none of these

Answer» Correct Answer - B
The given equation is meaningful, if sin x, cos x, tan x, cot x are positive and `"cos" x ne 1, "sin" x ne 1`.
Now,
`"log"_("cos"x) "tan" x +"log"_("sin"x)"cot" x = 0`
`rArr "log"_("cos"x) (("sin"x)/("cos" x)) + "log"_("sin"x) (("cos"x)/("sin"x)) =0`
`rArr "log"_("cos"x) "sin"x - "log"_("cos"x) "cos" x + "log"_("sin"x) "cos" x - "log"_("sin"x) "sin" x = 0`
`rArr "log"_("cos"x) "sin" x + "log"_("sin"x) "cos" x -2 =0`
`rArr "log"_("cos"x) "sin"x + (1)/("log"_("cos" x) "sin"x) -2 =0`
`rArr "log"_("cos"x) "sin"x = 1`
`rArr "sin" x = "cos" x rArr "tan" x = 1 rArr x=2n pi + (pi)/(4), n in Z`.


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