1. **State the problem:** We need to graph the quadratic function $$y = -x^2 - 10x - 21$$ and plot 5 points including the roots and the vertex.
2. **Formula and rules:** The quadratic function is in the form $$y = ax^2 + bx + c$$ where $$a = -1$$, $$b = -10$$, and $$c = -21$$.
3. **Find the vertex:** The vertex $$x$$-coordinate is given by $$x = -\frac{b}{2a} = -\frac{-10}{2 \times -1} = -\frac{-10}{-2} = -5$$.
4. **Calculate the vertex $$y$$-coordinate:**
$$y = -(-5)^2 - 10(-5) - 21 = -25 + 50 - 21 = 4$$.
So the vertex is at $$(-5, 4)$$.
5. **Find the roots:** Solve $$-x^2 - 10x - 21 = 0$$.
Multiply both sides by $$-1$$ to simplify:
$$\cancel{-1} \times (-x^2 - 10x - 21) = \cancel{-1} \times 0$$
$$x^2 + 10x + 21 = 0$$.
6. **Factor the quadratic:**
$$x^2 + 10x + 21 = (x + 3)(x + 7) = 0$$.
7. **Roots are:**
$$x = -3$$ and $$x = -7$$.
8. **Calculate $$y$$ values for points near the vertex:**
- For $$x = -4$$:
$$y = -(-4)^2 - 10(-4) - 21 = -16 + 40 - 21 = 3$$.
- For $$x = -6$$:
$$y = -(-6)^2 - 10(-6) - 21 = -36 + 60 - 21 = 3$$.
9. **Points to plot:**
- Roots: $$(-3, 0)$$ and $$(-7, 0)$$
- Vertex: $$(-5, 4)$$
- Additional points: $$(-4, 3)$$ and $$(-6, 3)$$
These 5 points show the shape of the parabola.
**Final answer:** The parabola opens downward with vertex at $$(-5, 4)$$ and roots at $$(-3, 0)$$ and $$(-7, 0)$$. Additional points $$(-4, 3)$$ and $$(-6, 3)$$ help plot the curve.
Quadratic Graph 78B795
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