Question

Consider $$f\left( x \right) = {x^2} - 3x + a + \frac{1}{a},a \in R - \left\{ 0 \right\},$$        such that $$f\left( 3 \right) > 0$$  and $$f\left( 2 \right) \leqslant 0.$$  If $$\alpha $$ and $$\beta $$ are the roots of equation $$f\left( x \right) = 0 $$   then the value of $${\alpha ^2} + {\beta ^2}$$  is equal to

A. greater than 11
B. less than 5
C. 5  
D. depends upon $$a$$ and $$a$$ cannot be determined
Answer :   5
Solution :
$$\eqalign{ & f\left( x \right) = {x^2} - 3x + a + \frac{1}{a};f\left( 3 \right) = 9 - 9 + a + \frac{1}{a} > 0 \cr & \Rightarrow a + \frac{1}{a} > 0 \cr & \Rightarrow a > 0 \cr & f\left( 2 \right) = 4 - 6 + a + \frac{1}{a} \leqslant 0 \cr & \Rightarrow \frac{{{a^2} - 2a + 1}}{a} \leqslant 0 \cr & \Rightarrow \frac{{{{\left( {a - 1} \right)}^2}}}{a} \leqslant 0 \cr & \Rightarrow a = 1 \cr} $$
Therefore, $$f\left( x \right) = {x^2} - 3x + 2 = 0$$     has root 1 and 2.
$$\therefore {\alpha ^2} + {\beta ^2} = 5$$

Releted MCQ Question on
Algebra >> Quadratic Equation

Releted Question 1

If $$\ell ,m,n$$  are real, $$\ell \ne m,$$  then the roots by the equation: $$\left( {\ell - m} \right){x^2} - 5\left( {\ell + m} \right)x - 2\left( {\ell - m} \right) = 0$$         are

A. Real and equal
B. Complex
C. Real and unequal
D. None of these
Releted Question 2

The equation $$x + 2y + 2z = 1{\text{ and }}2x + 4y + 4z = 9{\text{ have}}$$

A. Only one solution
B. Only two solutions
C. Infinite number of solutions
D. None of these
Releted Question 3

Let $$a > 0, b > 0$$    and $$c > 0$$ . Then the roots of the equation $$a{x^2} + bx + c = 0$$

A. are real and negative
B. have negative real parts
C. both (A) and (B)
D. none of these
Releted Question 4

Both the roots of the equation $$\left( {x - b} \right)\left( {x - c} \right) + \left( {x - a} \right)\left( {x - c} \right) + \left( {x - a} \right)\left( {x - b} \right) = 0$$           are always

A. positive
B. real
C. negative
D. none of these.

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Quadratic Equation


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