Function Analysis 7E1119
1. Stating the problem: We have the function $$y = \frac{4}{-x - 2} - 4$$ and need to find:
1.1 The domain of the function.
1.2 The roots (zeros) of the function.
1.3 The intervals where the function is positive.
2. Domain determination:
The function is a rational function with denominator $$-x - 2$$.
The denominator cannot be zero because division by zero is undefined.
Set denominator equal to zero:
$$-x - 2 = 0$$
Solve for $$x$$:
$$-x = 2 \implies x = -2$$
So, the domain is all real numbers except $$x = -2$$.
Domain: $$\{x \in \mathbb{R} \mid x \neq -2\}$$.
3. Finding roots (where $$y=0$$):
Set the function equal to zero:
$$0 = \frac{4}{-x - 2} - 4$$
Add 4 to both sides:
$$4 = \frac{4}{-x - 2}$$
Multiply both sides by $$-x - 2$$:
$$4(-x - 2) = 4$$
Simplify left side:
$$-4x - 8 = 4$$
Add 8 to both sides:
$$-4x = 12$$
Divide both sides by -4:
$$x = -3$$
Check that $$x = -3$$ is in the domain (it is).
So, the root is $$x = -3$$.
4. Finding where the function is positive ($$y > 0$$):
Start with:
$$\frac{4}{-x - 2} - 4 > 0$$
Add 4 to both sides:
$$\frac{4}{-x - 2} > 4$$
Multiply both sides by $$-x - 2$$, but remember to reverse inequality if $$-x - 2 < 0$$.
Consider two cases:
Case 1: $$-x - 2 > 0 \implies -x > 2 \implies x < -2$$
Multiply inequality by positive number (no sign change):
$$4 > 4(-x - 2)$$
Simplify right side:
$$4 > -4x - 8$$
Add $$4x$$ and $$8$$ to both sides:
$$4 + 4x + 8 > 0 \implies 4x + 12 > 0$$
Subtract 12:
$$4x > -12$$
Divide by 4:
$$x > -3$$
Combine with domain condition $$x < -2$$:
$$-3 < x < -2$$
Case 2: $$-x - 2 < 0 \implies x > -2$$
Multiply inequality by negative number (reverse inequality):
$$4 < 4(-x - 2)$$
Simplify right side:
$$4 < -4x - 8$$
Add $$4x$$ and $$8$$ to both sides:
$$4 + 4x + 8 < 0 \implies 4x + 12 < 0$$
Subtract 12:
$$4x < -12$$
Divide by 4:
$$x < -3$$
Combine with domain condition $$x > -2$$:
No $$x$$ satisfies $$x > -2$$ and $$x < -3$$ simultaneously.
Therefore, the function is positive only on the interval:
$$(-3, -2)$$.
Final answers:
- Domain: $$\{x \in \mathbb{R} \mid x \neq -2\}$$
- Root: $$x = -3$$
- Positive values: $$x \in (-3, -2)$$