For the next two (2) items that follow:
Consider the following 1. α + β + αβ > 0 2. α 2β + β 2α > 0
2 only
We are given a quadratic equation \(x^2 + bx + c = 0\), where \(b > 0\) and \(c < 0\). Let the roots of this equation be \(\alpha\) and \(\beta\), with the condition that \(\alpha < \beta\).
For a general quadratic equation \(ax^2 + bx + c = 0\), Vieta's formulas relate the coefficients to the sum and product of the roots. For our equation \(x^2 + bx + c = 0\) (where \(a=1\)), the formulas are:
We are given that \(b > 0\) and \(c < 0\).
The product of the roots being negative (\(\alpha \beta < 0\)) implies that the two roots must have opposite signs. One root is positive, and the other is negative. Given that \(\alpha < \beta\), \(\alpha\) must be the negative root and \(\beta\) must be the positive root.
Let's substitute the expressions for the sum and product of roots from Vieta's formulas into the statement:
\(\alpha + \beta + \alpha\beta = (-b) + (c) = -b + c\)
We are given that \(b > 0\), which means \(-b\) is a negative number. We are also given that \(c < 0\), which means \(c\) is a negative number.
The sum of two negative numbers is always negative.
So, \(-b + c < 0\).
The statement \(\alpha + \beta + \alpha\beta > 0\) is equivalent to \(-b + c > 0\). Based on our analysis, this is false.
Therefore, Statement 1 is incorrect.
Let's factor the expression \(\alpha^2\beta + \beta^2\alpha\). We can factor out the common term \(\alpha\beta\):
\(\alpha^2\beta + \beta^2\alpha = \alpha\beta(\alpha + \beta)\)
Now, substitute the expressions for the product and sum of roots from Vieta's formulas:
\(\alpha\beta(\alpha + \beta) = (c)(-b) = -bc\)
We are given that \(b > 0\) and \(c < 0\).
The product \(bc\) will be the product of a positive number (\(b\)) and a negative number (\(c\)). The product of a positive and a negative number is always negative. So, \(bc < 0\).
Now consider \(-bc\). Since \(bc\) is negative, \(-bc\) will be the negative of a negative number, which is positive.
So, \(-bc > 0\).
The statement \(\alpha^2\beta + \beta^2\alpha > 0\) is equivalent to \(-bc > 0\). Based on our analysis, this is true.
Therefore, Statement 2 is correct.
Based on our evaluation:
Thus, only Statement 2 is correct.
| Statement | Expression | Equivalent Expression using \(b\) and \(c\) | Evaluation (\(b>0, c<0\)) | Correctness |
|---|---|---|---|---|
| 1 | \(\alpha + \beta + \alpha\beta\) | \(-b + c\) | Sum of two negative numbers is negative. \(-b+c < 0\). | Incorrect |
| 2 | \(\alpha^2\beta + \beta^2\alpha\) | \(-bc\) | Product of positive (\(b\)) and negative (\(c\)) is negative (\(bc<0\)). Negative of negative is positive (\(-bc > 0\)). | Correct |
Understanding the relationship between the coefficients and the roots of a quadratic equation is fundamental. Vieta's formulas provide a direct link, allowing us to find the sum and product of roots without explicitly calculating the roots themselves.
Key points about roots based on coefficients:
In this problem, since \(\alpha\) and \(\beta\) are given as real roots, the discriminant \(b^2 - 4c\) must be greater than or equal to 0. Since \(b > 0\) (\(b^2 > 0\)) and \(c < 0\) (\(-4c > 0\)), \(b^2 - 4c\) is definitely positive, confirming two distinct real roots.
If p and q are the non-zero roots of the equation x 2+ px + q = 0, then how many possible values can q have?
The quadratic equation 3x 2- (k 2+ 5k)x + 3k 2- 5k = 0 has real roots of equal magnitude and opposite sign. Which one of the following is correct?
Under what condition does the above equation have real roots?
Under what condition is \(\frac{1}{{{{\rm{\alpha }}^2}}} + \frac{1}{{{{\rm{\beta }}^2}}} < 1?\)
If both the roots of the equation x 2– 2kx + k 2- 4 = 0 lie between – 3 and 5, then which one of the following is correct?
If c > 0 and 4a + c < 2b, then ax 2– bx + c = 0 has a root in which one of the following intervals?
The roots α and β of a quadratic equation, satisfy the relations α + β = α 2+ β 2and αβ = α 2β 2. What is the number of such quadratic equations?
Consider the following:
1. β < - α
2. β < |α|
Which of the above is/are correct?