Home
Class 11
MATHS
Let p, q, r in R and r gt p gt 0. If the...

Let p, q, r `in` R and `r gt p gt 0`. If the quadratic equation `px^(2) + qx + r = 0` has two complex roots `alpha and beta`, then `|alpha|+|beta|`, is

A

less than 2 but not equal to 1

B

equal to 2

C

equal to 1

D

greater than 2

Text Solution

AI Generated Solution

The correct Answer is:
To solve the problem, we need to analyze the quadratic equation given by \( px^2 + qx + r = 0 \) under the conditions that \( r > p > 0 \) and that the roots \( \alpha \) and \( \beta \) are complex. ### Step-by-Step Solution: 1. **Understanding the Nature of Roots**: Since the roots are complex, the discriminant of the quadratic equation must be negative. The discriminant \( D \) is given by: \[ D = q^2 - 4pr \] For the roots to be complex, we need: \[ D < 0 \implies q^2 < 4pr \] 2. **Using the Properties of Roots**: The roots \( \alpha \) and \( \beta \) can be expressed in terms of their product and sum: - The sum of the roots \( \alpha + \beta = -\frac{q}{p} \) - The product of the roots \( \alpha \beta = \frac{r}{p} \) 3. **Finding the Modulus of the Roots**: Since \( \alpha \) and \( \beta \) are complex, we can express them in terms of their modulus: \[ \alpha = a + i b \quad \text{and} \quad \beta = a - i b \] where \( a \) and \( b \) are real numbers. The modulus of the roots is given by: \[ |\alpha| = \sqrt{a^2 + b^2} \quad \text{and} \quad |\beta| = \sqrt{a^2 + b^2} \] 4. **Relating Modulus to Product**: The product of the roots can be expressed as: \[ |\alpha| \cdot |\beta| = |\alpha|^2 = \frac{r}{p} \] Since \( r > p > 0 \), we have: \[ |\alpha|^2 = \frac{r}{p} > 1 \implies |\alpha| > 1 \] Similarly, since \( \beta \) is the conjugate of \( \alpha \), we have: \[ |\beta|^2 = \frac{r}{p} > 1 \implies |\beta| > 1 \] 5. **Summing the Moduli**: Now, we can add the moduli: \[ |\alpha| + |\beta| > 1 + 1 = 2 \] ### Conclusion: Thus, we conclude that: \[ |\alpha| + |\beta| > 2 \]

To solve the problem, we need to analyze the quadratic equation given by \( px^2 + qx + r = 0 \) under the conditions that \( r > p > 0 \) and that the roots \( \alpha \) and \( \beta \) are complex. ### Step-by-Step Solution: 1. **Understanding the Nature of Roots**: Since the roots are complex, the discriminant of the quadratic equation must be negative. The discriminant \( D \) is given by: \[ D = q^2 - 4pr ...
Promotional Banner

Topper's Solved these Questions

  • QUADRATIC EXPRESSIONS AND EQUATIONS

    OBJECTIVE RD SHARMA ENGLISH|Exercise Section I - Solved Mcqs|123 Videos
  • QUADRATIC EXPRESSIONS AND EQUATIONS

    OBJECTIVE RD SHARMA ENGLISH|Exercise Section II - Assertion Reason Type|22 Videos
  • PROBABILITY

    OBJECTIVE RD SHARMA ENGLISH|Exercise Chapter Test|45 Videos
  • SEQUENCES AND SERIES

    OBJECTIVE RD SHARMA ENGLISH|Exercise Chapter Test|59 Videos

Similar Questions

Explore conceptually related problems

Let a,b,c in R and a gt 0 . If the quadratic equation ax^(2) +bx +c=0 has two real roots alpha and beta such that alpha gt -1 and beta gt 1 , then show that 1 + |b/a| + c/a gt 0

Let p, q in R . If 2- sqrt3 is a root of the quadratic equation, x^(2)+px+q=0, then

Given the alpha + beta are the roots of the quadratic equation px^(2) + qx + 1 = 0 find the value of alpha^(3)beta^(2) + alpha^(2)beta^(3) .

If alpha and beta are the roots of the quadratic equation px^(2)+qx+1 , Then the value of alphabeta+alpha^(2)beta^(2) is

Let alpha, beta are two real roots of equation x ^(2) + px+ q =0, p ,q, in R, q ne 0. If the quadratic equation g (x) =0 has two roots alpha + (1)/(alpha) , beta + (1)/(beta) such that sum of its roots is equal to product of roots, then number of integral values g can attain is :

The roots alpha and beta of the quadratic equation px^(2) + qx + r = 0 are real and of opposite signs. The roots of alpha(x-beta)^(2) + beta(x-alpha)^(2) = 0 are:

If alpha and beta are the roots of the quadratic equation x^(2) + px + q = 0 , then form the quadratic equation whose roots are alpha + (1)/(beta), beta + (1)/(alpha)

Let alpha and beta be the roots of equation px^2 + qx + r = 0 , p != 0 .If p,q,r are in A.P. and 1/alpha+1/beta=4 , then the value of |alpha-beta| is :

Let alpha and beta be the roots of equation px^2 + qx + r = 0 , p != 0 .If p,q,r are in A.P. and 1/alpha+1/beta=4 , then the value of |alpha-beta| is :

If the equations px^2+2qx+r=0 and px^2+2rx+q=0 have a common root then p+q+4r=

OBJECTIVE RD SHARMA ENGLISH-QUADRATIC EXPRESSIONS AND EQUATIONS -Chapter Test
  1. Let p, q, r in R and r gt p gt 0. If the quadratic equation px^(2) + q...

    Text Solution

    |

  2. The set of values of a for which x^2+ax+sin^(-1)(x^2-4x+5)+cos^(-1)(x^...

    Text Solution

    |

  3. The set of possible values of lambda for which x^2-(lambda^2-5 lambda...

    Text Solution

    |

  4. The equation (a + 2)x^2 + (a-3)x = 2a - 1, a != -2 has roots rational ...

    Text Solution

    |

  5. If cos alpha, sin beta, sin alpha are in increasing G.P. , then roots ...

    Text Solution

    |

  6. If alpha,beta are roots of x^2-3x+a=0,a in Ra n dalpha<1<beta, then f...

    Text Solution

    |

  7. If the equations ax^2+bx+c=0 and cx^2+bx+a=0, a!=c have a negative com...

    Text Solution

    |

  8. If the roots of the equation x^3-12x^2 +39x -28 =0 are in AP, then the...

    Text Solution

    |

  9. If the roots of a1x^2 + b1x+ c1 = 0 are alpha1 ,beta 1 and those o...

    Text Solution

    |

  10. If the roots of the equation ax^(2)-4x+a^(2)=0 are imaginery and the s...

    Text Solution

    |

  11. If a, b, c are positive real numbers, then the roots of the equation a...

    Text Solution

    |

  12. If the absolute value of the difference of the roots of the equation x...

    Text Solution

    |

  13. If alpha, beta be roots of the equation 375x ^(2) -25x-2=0 and s (n) =...

    Text Solution

    |

  14. The quadratic equation x^(2) + (a^(2) - 2) x - 2a^(2) and x^(2) - 3x +...

    Text Solution

    |

  15. The roots of ax^(2) +bx +c =0 " whose " a ne 0, b ,c in R , " are non...

    Text Solution

    |

  16. The value of m for which the equation x^3-mx^2+3x-2=0 has two roots ...

    Text Solution

    |

  17. If the equation formed by decreasing each root of the a x^2+b x+c=0 by...

    Text Solution

    |

  18. If the roots of the equation ax^2-bx-c=0 are changed by same quantity ...

    Text Solution

    |

  19. If x^2-2rprx+r=0; r=1, 2,3 are three quadratic equations of which each...

    Text Solution

    |

  20. If x ^(2) + px +1 is a factor of ax ^(3) + bx +c, then:

    Text Solution

    |

  21. If (x-1)^3 is a factor of x^4+ax^3+bx^2+cx-1=0 then the other factor ...

    Text Solution

    |