Vertex Y Intercept
1. **State the problem:** We are given the quadratic expression $$(x-2)(x+4)$$ and need to find its vertex and y-intercept without graphing.
2. **Expand the expression:** Use the distributive property (FOIL) to expand:
$$ (x-2)(x+4) = x^2 + 4x - 2x - 8 = x^2 + 2x - 8 $$
3. **Find the y-intercept:** The y-intercept occurs when $x=0$.
Substitute $x=0$:
$$ y = 0^2 + 2(0) - 8 = -8 $$
So, the y-intercept is at the point $$(0, -8)$$.
4. **Convert the quadratic to vertex form:** The vertex form is $$y = a(x-h)^2 + k$$, where $$(h,k)$$ is the vertex.
We use completing the square:
$$ y = x^2 + 2x - 8 $$
Take the coefficient of $x$, which is 2, divide by 2 and square it:
$$ \left(\frac{2}{2}\right)^2 = 1 $$
Add and subtract 1 inside the equation:
$$ y = (x^2 + 2x + 1) - 1 - 8 = (x+1)^2 - 9 $$
5. **Identify the vertex:** From vertex form
$$ y = (x+1)^2 - 9 $$
The vertex is $$(-1, -9)$$.
**Final answers:**
- Vertex: $$(-1, -9)$$
- Y-intercept: $$(0, -8)$$