Murray Murray
02/12/2023 · Primary School
16. \( x^{2}+3 x-m-2=0, \operatorname{C} K(S S)=\left\{x_{1}, x_{2}\right\} \) \( 2 x_{1}+x_{2}=-4 \Rightarrow m=? \)
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Step-by-step Solution
To solve for \( m \) in the equation \( x^2 + 3x - m - 2 = 0 \) given the condition \( 2x_1 + x_2 = -4 \), we start by using Vieta's formulas. According to Vieta's, for a quadratic equation of the form \( ax^2 + bx + c = 0 \), the sum and product of the roots \( x_1 \) and \( x_2 \) are given by:
\[
x_1 + x_2 = -\frac{b}{a} \quad \text{and} \quad x_1 x_2 = \frac{c}{a}
\]
In our case, we have:
- \( a = 1 \)
- \( b = 3 \)
- \( c = -m - 2 \)
Thus, we can write:
\[
x_1 + x_2 = -\frac{3}{1} = -3
\]
\[
x_1 x_2 = \frac{-m - 2}{1} = -m - 2
\]
Now, we also have the condition \( 2x_1 + x_2 = -4 \). We can express \( x_2 \) in terms of \( x_1 \):
\[
x_2 = -4 - 2x_1
\]
Next, we substitute \( x_2 \) into the equation for the sum of the roots:
\[
x_1 + (-4 - 2x_1) = -3
\]
Simplifying this gives:
\[
x_1 - 4 - 2x_1 = -3
\]
\[
-x_1 - 4 = -3
\]
\[
-x_1 = 1 \quad \Rightarrow \quad x_1 = -1
\]
Now, substituting \( x_1 = -1 \) back into the equation for \( x_2 \):
\[
x_2 = -4 - 2(-1) = -4 + 2 = -2
\]
Now we have the roots \( x_1 = -1 \) and \( x_2 = -2 \). We can now find \( m \) using the product of the roots:
\[
x_1 x_2 = -m - 2
\]
\[
(-1)(-2) = -m - 2
\]
\[
2 = -m - 2
\]
Solving for \( m \):
\[
2 + 2 = -m
\]
\[
4 = -m \quad \Rightarrow \quad m = -4
\]
Thus, the value of \( m \) is
\[
\boxed{-4}
\]
Quick Answer
The value of \( m \) is -4.
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