Marsh Valdez
08/30/2023 · Senior High School
Solve the inequality \( -2 x^{2}-6 x-4<0 \) The solution has form: \[ \mathrm{A}<\mathrm{x}<\mathrm{B} \] Where \( \mathrm{A}=\square \) or \( \mathrm{x}>\mathrm{B} \) and \( \mathrm{B}=\square \)
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Step-by-step Solution
To solve the inequality \( -2x^2 - 6x - 4 < 0 \), we first rewrite it in a more standard form by multiplying through by -1 (which reverses the inequality):
\[
2x^2 + 6x + 4 > 0
\]
Next, we can simplify this expression by dividing all terms by 2:
\[
x^2 + 3x + 2 > 0
\]
Now, we will factor the quadratic expression:
\[
x^2 + 3x + 2 = (x + 1)(x + 2)
\]
Thus, we need to solve the inequality:
\[
(x + 1)(x + 2) > 0
\]
To find the critical points, we set the factors equal to zero:
\[
x + 1 = 0 \quad \Rightarrow \quad x = -1
\]
\[
x + 2 = 0 \quad \Rightarrow \quad x = -2
\]
These critical points divide the number line into intervals. We will test the sign of the product \( (x + 1)(x + 2) \) in each of the intervals:
1. **Interval \( (-\infty, -2) \)**: Choose \( x = -3 \):
\[
(-3 + 1)(-3 + 2) = (-2)(-1) = 2 > 0
\]
2. **Interval \( (-2, -1) \)**: Choose \( x = -1.5 \):
\[
(-1.5 + 1)(-1.5 + 2) = (-0.5)(0.5) = -0.25 < 0
\]
3. **Interval \( (-1, \infty) \)**: Choose \( x = 0 \):
\[
(0 + 1)(0 + 2) = (1)(2) = 2 > 0
\]
Now we summarize the results:
- The product \( (x + 1)(x + 2) > 0 \) in the intervals \( (-\infty, -2) \) and \( (-1, \infty) \).
- The product \( (x + 1)(x + 2) < 0 \) in the interval \( (-2, -1) \).
Thus, the solution to the inequality \( -2x^2 - 6x - 4 < 0 \) is:
\[
-2 < x < -1
\]
In the required form, we have:
\[
\mathrm{A} = -2 \quad \text{and} \quad \mathrm{B} = -1
\]
So the final answer is:
\[
\mathrm{A} = -2, \quad \mathrm{B} = -1
\]
Quick Answer
The solution to the inequality is \( x \) in the interval \( (-2, -1) \). Therefore, \( \mathrm{A} = -2 \) and \( \mathrm{B} = -1 \).
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