Solve the math problems in the attached image.

Understand the Problem
The image contains multiple math questions related to polynomials and quadratic equations. Specifically, they involve concepts such as zeros of polynomials, relationships between coefficients and roots, and conditions for real roots. We need to extract each question individually and categorize them accordingly.
Answer
1. (C) $qx^2 + px + 1$ 2. (B) $1-c$ 3. (C) $c<0$
Answer for screen readers
- (C) $qx^2 + px + 1$
- (B) $1-c$
- (C) $c<0$
Steps to Solve
Here's how to solve each of the three questions:
Question 1: If $\alpha$ and $\beta$ are the zeros of the polynomial $f(x) = x^2 + px + q$, then the polynomial having $\frac{1}{\alpha}$ and $\frac{1}{\beta}$ as its zeros is
- Find the sum and product of the new zeros
The new zeros are $\frac{1}{\alpha}$ and $\frac{1}{\beta}$. We need to find their sum and product:
Sum: $\frac{1}{\alpha} + \frac{1}{\beta} = \frac{\alpha + \beta}{\alpha \beta}$ Product: $\frac{1}{\alpha} \cdot \frac{1}{\beta} = \frac{1}{\alpha \beta}$
- Relate the original zeros to the coefficients of the polynomial
For the polynomial $f(x) = x^2 + px + q$, we know that the sum of the zeros is $-\frac{p}{1} = -p$ and the product of the zeros is $\frac{q}{1} = q$. So, $\alpha + \beta = -p$ and $\alpha \beta = q$.
- Substitute the relationships into the sum and product of new roots
Sum of new zeros: $\frac{\alpha + \beta}{\alpha \beta} = \frac{-p}{q}$ Product of new zeros: $\frac{1}{\alpha \beta} = \frac{1}{q}$
- Form the new polynomial
A polynomial with zeros $\frac{1}{\alpha}$ and $\frac{1}{\beta}$ can be written as: $x^2 - (\text{sum of zeros})x + (\text{product of zeros}) = 0$ $x^2 - (\frac{-p}{q})x + \frac{1}{q} = 0$ $x^2 + \frac{p}{q}x + \frac{1}{q} = 0$
Multiplying by $q$ to eliminate fractions, we get: $qx^2 + px + 1 = 0$
Thus, the required polynomial is $qx^2 + px + 1$.
Question 2: If $\alpha, \beta$ are the zeros of the polynomial $f(x) = x^2 - p(x+1) - c$, then $(\alpha + 1)(\beta + 1) = $
- Rewrite the polynomial in standard form
First, rewrite $f(x)$ as $f(x) = x^2 - px - p - c = x^2 - px - (p+c)$.
- Relate the zeros to the coefficients
From the polynomial $f(x)$, we have: $\alpha + \beta = p$ $\alpha \beta = -(p+c)$
- Expand the expression and substitute
Now, let's find $(\alpha + 1)(\beta + 1)$: $(\alpha + 1)(\beta + 1) = \alpha \beta + \alpha + \beta + 1$ Substitute the values we found: $= -(p+c) + p + 1$ $= -p - c + p + 1$ $= 1 - c$ So, $(\alpha + 1)(\beta + 1) = 1 - c$.
Question 3: If $f(x)=ax^2 + bx + c$ has no real zeros and $a + b + c < 0$, then
- Consider the condition of no real zeros
If the quadratic has no real zeros, then its discriminant must be negative. Discriminant, $D = b^2 - 4ac < 0$.
- Analyze $a + b + c < 0$
Notice that $f(1) = a(1)^2 + b(1) + c = a + b + c$. Since $a + b + c < 0$, we have $f(1) < 0$.
- Consider the sign of $a$
Since $f(x)$ has no real zeros, the parabola does not intersect the x-axis. Also, $f(1)<0$. This means that the parabola must open downwards, because if it opened upwards, $f(x)$ would have to cross the x-axis to have $f(1) < 0 $ which violates the problem condition of no real zeros i.e. no intersection with x-axis at all. Therefore, $a < 0$.
- Determine the sign of $c$
Since $a < 0$ and $b^2 - 4ac < 0$, we have $b^2 < 4ac$. Since $a < 0$, for $4ac$ to be greater than $b^2$, $c$ must also be negative. If $c$ was positive then $b^2 < 4ac$ would not hold because the sign of the expression is negative. If $c$ was zero then $b^2 < 4ac$ would not hold because $b^2$ is always positive or zero.
Thus, $c < 0$.
- (C) $qx^2 + px + 1$
- (B) $1-c$
- (C) $c<0$
More Information
These questions test the understanding of the relationships between the roots and coefficients of a quadratic equation, as well as the nature of the roots based on the discriminant and the sign of the quadratic expression.
Tips
- For the first question, a common mistake is not manipulating the sum and product of the new zeros correctly, or not relating them back to the coefficients of the original polynomial.
- For the second question, expanding $(\alpha + 1)(\beta + 1)$ incorrectly or not substituting the correct values for $\alpha + \beta$ and $\alpha \beta$ from the given polynomial are common errors.
- For the third question, not recognizing the implication of '$f(x)$ has no real zeros' and '$f(1) < 0$' on the sign of $a$ and $c$ can lead to an incorrect answer.
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