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Solve System of Inequalities \( y > 2x^2 - x - 1 \) and \( y > -3x + 2 \) (Algebra 2)
Mathematics (Algebra 2)
Grade 10 (High School)
Question Content
Sketch the solution to the system of inequalities \( y > 2x^2 - x - 1 \) and \( y > -3x + 2 \), then identify one solution to the system.
Correct Answer
One solution is (0, 3) (other valid points exist).
Detailed Solution Steps
1
1. Analyze \( y > 2x^2 - x - 1 \): The quadratic \( 2x^2 - x - 1 \) has vertex at \( \left( \frac{1}{4}, -1.125 \right) \) (opening upward). The inequality \( > \) means the parabola is dashed, and we shade above it.
2
2. Analyze \( y > -3x + 2 \): This is a linear line with slope \( -3 \) and \( y \)-intercept \( 2 \). The inequality \( > \) means the line is dashed, and we shade above it.
3
3. Identify the overlapping region (solution): The solution is where both shadings (above both the parabola and the line) overlap. Test the point \((0, 3)\):
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- For \( y > 2(0)^2 - 0 - 1 \): \( 3 > -1 \) (true).
5
- For \( y > -3(0) + 2 \): \( 3 > 2 \) (true). Thus, \((0, 3)\) is a solution.
Knowledge Points Involved
1
Graphing Quadratic Inequalities (Standard Form)
For \( y > ax^2 + bx + c \) ( \( a > 0 \) ), shade above the dashed parabola; the vertex is found using \( x = -\frac{b}{2a} \).
2
System of Two 'Greater Than' Inequalities
The solution to \( y > \text{quadratic} \) and \( y > \text{linear} \) is the region above the higher of the two graphs (where both shadings overlap).
3
Testing Points in Unbounded Regions
For unbounded solution regions (e.g., above both a parabola and line), test a point with positive \( y \)-value to confirm it lies above both graphs.
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