1. **State the problem:** Convert the quadratic function $y = x^2 + 2x - 5$ into vertex form and identify the axis of symmetry, extrema, and zeros.
2. **Recall the vertex form:** The vertex form of a quadratic is $$y = a(x-h)^2 + k$$ where $(h,k)$ is the vertex.
3. **Complete the square:** Start with $$y = x^2 + 2x - 5$$
4. Group the $x$ terms: $$y = (x^2 + 2x) - 5$$
5. To complete the square, take half of the coefficient of $x$, which is $2$, half is $1$, and square it: $1^2 = 1$.
6. Add and subtract $1$ inside the parentheses:
$$y = (x^2 + 2x + 1 - 1) - 5$$
7. Rewrite as:
$$y = ((x + 1)^2 - 1) - 5$$
8. Simplify:
$$y = (x + 1)^2 - 6$$
9. **Vertex:** The vertex is at $(-1, -6)$.
10. **Axis of symmetry:** The vertical line through the vertex, $x = -1$.
11. **Extrema:** Since $a=1 > 0$, the parabola opens upward, so the vertex is a minimum point at $y = -6$.
12. **Zeros:** Solve $y=0$:
$$0 = (x + 1)^2 - 6$$
$$ (x + 1)^2 = 6$$
$$x + 1 = \pm \sqrt{6}$$
$$x = -1 \pm \sqrt{6}$$
Approximations:
$$x \approx -1 + 2.45 = 1.45$$ and $$x \approx -1 - 2.45 = -3.45$$
13. **Y-intercept:** Set $x=0$:
$$y = (0 + 1)^2 - 6 = 1 - 6 = -5$$
14. **Summary:**
- Vertex form: $$y = (x + 1)^2 - 6$$
- Axis of symmetry: $$x = -1$$
- Minimum at $$(-1, -6)$$
- Zeros at $$x = -1 \pm \sqrt{6}$$
- Y-intercept at $(0, -5)$
These key features help graph the parabola accurately.
Vertex Form Bef486
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