Answer
To graph the quadratic function \( y = -2x^2 + 4x - 2 \), follow these steps:
1. **Identify the vertex form:**
Rewrite the equation as \( y = -2(x - 1)^2 \).
2. **Determine key features:**
- **Vertex:** \((1, 0)\)
- **Axis of symmetry:** \( x = 1 \)
- **Direction:** Opens downward
- **Intercepts:** \( y \)-intercept at \((0, -2)\) and \( x \)-intercept at \((1, 0)\)
3. **Plot the graph:**
- Draw the axis of symmetry at \( x = 1 \).
- Plot the vertex at \((1, 0)\) and the \( y \)-intercept at \((0, -2)\).
- Since the parabola opens downward, sketch the curve symmetrically around the axis of symmetry.
4. **Conclusion:**
The graph is a downward-opening parabola with vertex at \((1, 0)\), \( y \)-intercept at \((0, -2)\), and \( x \)-intercept at \((1, 0)\).
Solution
1. **Write the equation and factor the coefficient of \( x^2 \):**
The quadratic function is
\[
y = -2x^2 + 4x - 2.
\]
Factor out \(-2\) from the quadratic and linear terms:
\[
y = -2\left(x^2 - 2x\right) - 2.
\]
2. **Complete the square:**
To complete the square for \( x^2 - 2x \), take half the coefficient of \( x \) (which is \(-2\)) and square it:
\[
\left(\frac{-2}{2}\right)^2 = 1.
\]
Add and subtract \(1\) inside the parentheses:
\[
y = -2\left(x^2 - 2x + 1 - 1\right) - 2.
\]
Thus,
\[
y = -2\left[(x-1)^2 - 1\right] - 2.
\]
3. **Rewrite in vertex form:**
Distribute the \(-2\):
\[
y = -2(x-1)^2 + 2 - 2.
\]
Combine the constants:
\[
y = -2(x-1)^2.
\]
The vertex form is
\[
y = -2(x-1)^2.
\]
4. **Identify key features:**
- **Vertex:** The vertex of a quadratic in the form \( y = a(x-h)^2 + k \) is \((h, k)\). Here, the vertex is
\[
(1, 0).
\]
- **Axis of symmetry:** This is the vertical line \( x = h \), so
\[
x = 1.
\]
- **Direction of opening:** Since the coefficient \( a = -2 \) is negative, the parabola opens downward.
- **\( y \)-intercept:** Substitute \( x = 0 \) into the original equation:
\[
y = -2(0)^2 + 4(0) - 2 = -2,
\]
so the \( y \)-intercept is
\[
(0, -2).
\]
- **\( x \)-intercepts:** Set \( y = 0 \):
\[
0 = -2(x-1)^2.
\]
Divide by \(-2\):
\[
0 = (x-1)^2.
\]
Take the square root:
\[
x - 1 = 0 \quad \Rightarrow \quad x = 1.
\]
So there is a single \( x \)-intercept at
\[
(1, 0),
\]
which is also the vertex.
5. **Sketching the graph:**
- Plot the vertex at \((1, 0)\).
- Draw the axis of symmetry as the vertical line \( x = 1 \).
- Mark the \( y \)-intercept at \((0, -2)\).
- Note that the parabola touches the \( x \)-axis only at the vertex \((1, 0)\) and opens downward.
- You can choose additional points for a smoother curve; for example, for \( x = 2 \):
\[
y = -2(2-1)^2 = -2(1)^2 = -2,
\]
which gives the point \((2, -2)\). Its symmetric point about \( x=1 \) is \((0, -2)\) (which is already plotted as the \( y \)-intercept).
6. **Conclusion:**
The graph of
\[
y = -2x^2 + 4x - 2
\]
is a downward opening parabola with vertex \((1, 0)\), a single \( x \)-intercept at \((1, 0)\), and a \( y \)-intercept at \((0, -2)\).
The key features are summarized as:
- **Vertex:** \( (1, 0) \)
- **Axis of symmetry:** \( x = 1 \)
- **Opens:** Downward (since \( a < 0 \))
- **\( y \)-intercept:** \( (0, -2) \)
- **\( x \)-intercept:** \( (1, 0) \)
This completes the step-by-step solution for graphing the quadratic function.
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