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If A={x in R: x^(2)+6x-7 lt 0} and B={ x...

If `A={x in R: x^(2)+6x-7 lt 0} and B={ x in R: x^(2)+9x+14 gt 0}`, then which of the following is/are correct ?
1. `A cap B = {x in R: -2 x lt x lt 1}`
2. `AUB = {x in R: -7 lt x lt -2}`
Select the correct answer using the codes given below :

A

A) Only 1

B

B) Only 2

C

C) Both 1 and 2

D

D) Neither 1 nor 2

Text Solution

AI Generated Solution

The correct Answer is:
To solve the problem, we need to analyze the sets \( A \) and \( B \) based on the given inequalities. ### Step 1: Determine the set \( A \) The set \( A \) is defined as: \[ A = \{ x \in \mathbb{R} : x^2 + 6x - 7 < 0 \} \] First, we need to factor the quadratic expression \( x^2 + 6x - 7 \). 1. **Finding the roots:** We can use the quadratic formula: \[ x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} \] Here, \( a = 1, b = 6, c = -7 \). \[ x = \frac{-6 \pm \sqrt{6^2 - 4 \cdot 1 \cdot (-7)}}{2 \cdot 1} = \frac{-6 \pm \sqrt{36 + 28}}{2} = \frac{-6 \pm \sqrt{64}}{2} = \frac{-6 \pm 8}{2} \] This gives us the roots: \[ x = 1 \quad \text{and} \quad x = -7 \] 2. **Sign analysis:** We analyze the sign of \( x^2 + 6x - 7 \) in the intervals determined by the roots \( -7 \) and \( 1 \): - For \( x < -7 \): Both factors \( (x + 7) \) and \( (x - 1) \) are negative, so the product is positive. - For \( -7 < x < 1 \): \( (x + 7) \) is positive and \( (x - 1) \) is negative, so the product is negative. - For \( x > 1 \): Both factors are positive, so the product is positive. Thus, the solution to \( x^2 + 6x - 7 < 0 \) is: \[ A = (-7, 1) \] ### Step 2: Determine the set \( B \) The set \( B \) is defined as: \[ B = \{ x \in \mathbb{R} : x^2 + 9x + 14 > 0 \} \] 1. **Finding the roots:** We factor the quadratic expression \( x^2 + 9x + 14 \): \[ x^2 + 9x + 14 = (x + 7)(x + 2) \] The roots are: \[ x = -7 \quad \text{and} \quad x = -2 \] 2. **Sign analysis:** We analyze the sign of \( (x + 7)(x + 2) > 0 \): - For \( x < -7 \): Both factors are negative, so the product is positive. - For \( -7 < x < -2 \): \( (x + 7) \) is positive and \( (x + 2) \) is negative, so the product is negative. - For \( x > -2 \): Both factors are positive, so the product is positive. Thus, the solution to \( x^2 + 9x + 14 > 0 \) is: \[ B = (-\infty, -7) \cup (-2, \infty) \] ### Step 3: Find \( A \cap B \) To find \( A \cap B \), we look for the intersection of the intervals: - \( A = (-7, 1) \) - \( B = (-\infty, -7) \cup (-2, \infty) \) The intersection is: \[ A \cap B = (-7, 1) \cap \left( (-\infty, -7) \cup (-2, \infty) \right) = (-2, 1) \] ### Step 4: Find \( A \cup B \) To find \( A \cup B \), we combine the intervals: \[ A \cup B = (-7, 1) \cup \left( (-\infty, -7) \cup (-2, \infty) \right) = (-\infty, -7) \cup (-2, 1) \] ### Conclusion Now we can check the statements given in the question: 1. **Statement 1:** \( A \cap B = \{ x \in \mathbb{R} : -2 < x < 1 \} \) is **correct**. 2. **Statement 2:** \( A \cup B = \{ x \in \mathbb{R} : -7 < x < -2 \} \) is **incorrect**. ### Final Answer The correct answer is **1 only**.
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