NTA Abhyas JEE Main2020MathematicsQuadratic EquationPractice
The quadratic equation whose roots are the arithmetic mean and the harmonic mean of the roots of the equation x 2 + 7 x - 1 = 0 is
Options
- A14 x 2 + 14 x - 45 = 0
- B45 x 2 - 14 x + 14 = 0
- C14 x 2 + 45 x - 14 = 0
- D45 x 2 + 14 x - 45 = 0
Correct answer
C. 14 x 2 + 45 x - 14 = 0
Step-by-step solution
Let, α , β are the roots of the equation x 2 + 7 x - 1 = 0 ⇒ α + β = - 7 , α β = - 1 ⇒ A = α + β 2 = - 7 2 and H = 2 α β α + β = 2 - 1 - 7 = 2 7 . Now, equation whose roots are A and H is x 2 - A + H x + A H = 0 ⇒ x 2 - x - 7 2 + 2 7 + - 7 2 2 7 = 0 ⇒ x 2 + 45 14 x - 1 = 0 ⇒ 14 x 2 + 45 x - 14 = 0