1.

The value of a for which exactly one root of the equation `e^ax^2 - e^(2a)x + e^a -1` lies between 1 and 2 are given byA. In `((5-sqrt(17))/(4))lt a lt "In"((5+sqrt(17))/(4))`B. `0 lt a lt 100`C. In `(5)/(4) lt a lt "In"(10)/(3)`D. none of these

Answer» Correct Answer - A
Let `f(x) = e^(a) x^(2) - e^(2a) x + e^(a)-1`.
Clearly, y = f(x) represents a parabola opening upward. Also, Disc of f(x) = 0 is given by `D = e^(4a)-4e^(a)(e^(a) -10 = (e^(2a)-1) lt 0`
So, the roots are real and distinct for all a `in` R.
Thus, exactly one root will lie between 1 and 2, if f(1) f(2) `lt` 0
`rArr" "(e^(a)-e^(2a)+e^(a)-1)(e^(2a)-1)^(2) gt 0`
`rArr" "2e^(2a)-5e^(a) + 1 lt 0`
`rArr" "(5-sqrt(17))/(4)lt e^(a) lt (5+sqrt(17))/(4) rArr "In"(5-sqrt(17))/(4) lt a lt "In"(5+sqrt(17))/(4)`


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