1.

The number of integral values of a for which `x^(2) - (a-1) x+3 = 0` has both roots positive and `x^(2) + 3x + 6 - a = 0` has both roots negative is

Answer» Correct Answer - B
Let `f(x) = x^(2) - (a-1) x + 3 and g(x) = x^(2) + 3x + 6 - a`.
If `f(x)=0` has both positive roots, then
`f(0) gt 0, (a-1)^(2) - 12 gt 0 and, (a-1)/(2) gt 0`
`rArr" "(a-1-2 sqrt(3))(a-1+2 sqrt(3)) gt 0 and a gt 1`
`rArr" "a gt 1 + 2 sqrt(3)" "...(i)`
If g(x) = 0 has both roots negative, then `g(0) gt 0, -(3)/(2) lt 0 and, 9-4 (6-a)gt 0`
`rArr" "6-a gt 0 and 4a - 15 gt 0`
`rArr" "a lt 6 and a gt (15)/(4) rArr (15)/(4) lt a lt 6" "...(ii)`
From (i) and (ii), we have
`1+2 sqrt(3) lt a lt 6 rArr a = 5" "[because "a is an integer"]`
Thus, there is only one integral value of a.


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