The Real Values Of a for Which The Sum Of The Squares Of The Roots Of The Equation x2 – (a – 2) x – a – 1 = 0 Assume The Least Value Is

Why Kaysons ?

Video lectures

Access over 500+ hours of video lectures 24*7, covering complete syllabus for JEE preparation.

Online Support

Practice over 30000+ questions starting from basic level to JEE advance level.

Live Doubt Clearing Session

Ask your doubts live everyday Join our live doubt clearing session conducted by our experts.

National Mock Tests

Give tests to analyze your progress and evaluate where you stand in terms of your JEE preparation.

Organized Learning

Proper planning to complete syllabus is the key to get a decent rank in JEE.

Test Series/Daily assignments

Give tests to analyze your progress and evaluate where you stand in terms of your JEE preparation.

SPEAK TO COUNSELLOR ? CLICK HERE

Question

The real values of a for which the sum of the squares of the roots of the equation x2 – (a – 2) x – a – 1 = 0 assume the least value is

Solution

Correct option is

1

 

Discriminant of the equation is (a – 2)2 + 4(a + 1)

              = a2 – 4a + 4 + 4a + 4

              = a2 + 8 > 0 as a Ïµ R.

∴ Roots of the given equation are real. Let these roots be α and β

Then α + β = a – 2, αβ = – (α + 1).

We have

         α2 + β 2 = (α + β)2 - 2αβ = (α - 2)2 + 2 (α + 1)

                        = a2 – 4a + 4 + 2a + 2 = a2 – 2a + 6

                        = (a – 1)2 + 5

Thus, α2 + β 2 is least when a =1.

SIMILAR QUESTIONS

Q1

If one root of the equation x2 + px + 12 = 0 is 4, while the equation x2 +px + q = 0 has equal roots, the value of q is

Q2

If x2 + px + 1 is a factor of ax2 + bx + c, then

Q3

If 8, 2 are the roots of x2 + ax + β = 0 and 3, 3 are the roots of x2 + α xb = 0 then the roots of x2 + ax + b = 0 are

Q4

The number of real roots of 

Q5

The product of real of the equation  

              is

Q6

Sum of the non – real roots of 

 

Q7

If tan A and tan B are the roots of the quadratic equation x2 – px + q = 0, then value of sin2 (A + B) is

Q8

If x Ïµ R, the number of solution of  = 1 is

Q9

If lmn are real, l + m ≠ 0, then the roots of the equation

         (l + m)x2 – 3(l – m)x – 2 (l + m) = 0 are

Q10

If p and q are distinct primes and x2 – px + = 0 has distinct positive roots, then p + equals