1. **State the problem:** We have a quadratic function $y = x^2 + bx + c$ with points $P(-3, -9)$ and $Q(2, -4)$ on the curve. We need to find $b$ and $c$, the y-intercept, and the x-intercepts.
2. **Form equations using the points:** Substitute $P(-3, -9)$ into $y = x^2 + bx + c$:
$$-9 = (-3)^2 + b(-3) + c = 9 - 3b + c$$
Rearranged:
$$-9 = 9 - 3b + c$$
$$-9 - 9 = -3b + c$$
$$-18 = -3b + c$$
Substitute $Q(2, -4)$:
$$-4 = 2^2 + 2b + c = 4 + 2b + c$$
Rearranged:
$$-4 - 4 = 2b + c$$
$$-8 = 2b + c$$
3. **Write the system of equations:**
$$\begin{cases}
-18 = -3b + c \\
-8 = 2b + c
\end{cases}$$
4. **Solve the system:** Subtract second from first:
$$-18 - (-8) = (-3b + c) - (2b + c)$$
$$-10 = -3b + c - 2b - c$$
$$-10 = -5b$$
Divide both sides by $-5$:
$$\cancel{-10} / \cancel{-5} = \cancel{-5b} / \cancel{-5}$$
$$2 = b$$
Substitute $b=2$ into $-8 = 2b + c$:
$$-8 = 2(2) + c$$
$$-8 = 4 + c$$
$$c = -8 - 4 = -12$$
5. **Y-intercept:** The curve intersects the y-axis where $x=0$:
$$y = 0^2 + 2(0) + (-12) = -12$$
So the y-intercept is $(0, -12)$.
6. **Find x-intercepts:** Set $y=0$:
$$0 = x^2 + 2x - 12$$
Use quadratic formula:
$$x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} = \frac{-2 \pm \sqrt{2^2 - 4(1)(-12)}}{2} = \frac{-2 \pm \sqrt{4 + 48}}{2} = \frac{-2 \pm \sqrt{52}}{2}$$
Simplify:
$$\sqrt{52} = \sqrt{4 \times 13} = 2\sqrt{13}$$
So:
$$x = \frac{-2 \pm 2\sqrt{13}}{2} = -1 \pm \sqrt{13}$$
Calculate approximate values:
$$x_1 = -1 + 3.6 = 2.6$$
$$x_2 = -1 - 3.6 = -4.6$$
**Final answers:**
- $b = 2$
- $c = -12$
- Y-intercept: $(0, -12)$
- X-intercepts: $(2.6, 0)$ and $(-4.6, 0)$ (to one decimal place)
Quadratic Parameters E40350
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