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JEE MAIN 2019
09-01-2019__S2
Question
If both the roots of the quadratic equation $x^2-m x+4=0$ are real and distinct and they lie in the interval $[1,5]$ then m lies in the interval:
Select the correct option:
A
(–5, –4)
B
(3, 4)
C
(4, 5)
D
(5, 6)
✓ Correct! Well done.
✗ Incorrect. Try again or view the solution.
Solution
Given quadratic equation is: $x^2-m x+4=0$ Both the roots are real and distinct. $$ \begin{aligned} & \therefore m^2-4 \cdot 1 \cdot 4>0 \\ & \therefore(m-4)(m+4)>0 \\ & \therefore m \in(-\infty,-4) \cup(4, \infty) \end{aligned} $$ ∵ both roots lies in [1, 5] $$ \begin{aligned} & \therefore-\frac{-m}{2} \in(1,5) \\ & \Rightarrow m \in(2,10) \end{aligned} $$ And 1 $(1-m+4)>0 \Rightarrow m<5 m \in(-x, 5)$ And $1 \cdot(25-5 m+4)>0=$ $$ m<\frac{29}{5} $$ $$ \therefore \quad m \in\left(-x, \frac{29}{5}\right) $$
Question Tags
JEE Main
Mathematics
Medium
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