1.

Let `(sin a) x^(2) + (sin a) x + 1 - cos a = 0`. The set of values of a for which roots of this equation are real and distinct, isA. `(0, 2 tan^(-1)(1)/(4))`B. `(o, (2pi)/(3))`C. `(0, pi)`D. `(0, 2pi)`

Answer» Correct Answer - A
The roots of the given equation will be real and distinct, iff
`sin^(2) a - 4 sin a(1-cos a) gt 0`
`rArr" "(1-cos a){1+cos a - 4 sin a} gt 0`
`rArr" "2 cos^(2)(a)/(2)-8 sin (a)/(2) cos (a)/(2) gt 0" "[because 1-cos a gt 0]`
`rArr" "2 cos^(2)(a)/(2)(1-4"tan"(a)/(2))gt 0`
`rArr" "4 "tan"(a)/(2) lt 1 rArr -(pi)/(2) lt (a)/(2) lt "tan"^(-1)(1)/(4) rArr -pi lt a lt 2 "tan"^(-1)(1)/(4)`
Hence, option (a) is correct.


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