Mathematics
Grade 12
15 min
Graph a quadratic function
Graph a quadratic function
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1
Introduction & Learning Objectives
Learning Objectives
Identify the key features of a parabola (vertex, axis of symmetry, intercepts, concavity) from its equation.
Graph a quadratic function given in standard form, f(x) = ax^2 + bx + c.
Graph a quadratic function given in vertex form, f(x) = a(x-h)^2 + k.
Determine the vertex of a parabola algebraically using the formula x = -b/(2a).
Verify the vertex of a parabola by finding where the first derivative equals zero (f'(x) = 0).
Determine the domain and range of a quadratic function from its graph and equation.
Accurately sketch the graph of a quadratic function by plotting its vertex and intercepts.
Ever wondered about the perfect arc of a basketball shot or the path of a satellite? 🏀 That's a parabola, the beautiful curve described by a quadratic...
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Key Concepts & Vocabulary
TermDefinitionExample
ParabolaThe distinctive U-shaped curve that represents a quadratic function on a graph.The graph of y = x^2 is a simple parabola that opens upwards with its lowest point at the origin (0,0).
VertexThe highest or lowest point on a parabola. It is the turning point of the graph.For the parabola y = (x-3)^2 + 5, the vertex is at the point (3, 5).
Axis of SymmetryA vertical line that passes through the vertex and divides the parabola into two mirror-image halves.For y = 2x^2 - 4x + 1, the vertex is at (1, -1), so the axis of symmetry is the vertical line x = 1.
Roots (or Zeros)The x-coordinates of the points where the parabola intersects the x-axis. These are the solutions to the equation f(x) = 0.The roots of f(x) = x^2 - 4 are x = 2 and x = -2, so the x-intercepts are...
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Core Formulas
Standard Form
f(x) = ax^2 + bx + c
The most common form of a quadratic function. The y-intercept is directly given by 'c'. The concavity is determined by the sign of 'a'.
Vertex Form
f(x) = a(x-h)^2 + k
This form directly reveals the vertex of the parabola, which is at the point (h, k). Be mindful that the formula has 'x-h', so the sign of h is often opposite of what it appears.
Vertex Formula (Algebraic)
x_{vertex} = -\frac{b}{2a}
Used with the standard form to find the x-coordinate of the vertex. To find the y-coordinate, substitute this x-value back into the original function: y_{vertex} = f(-\frac{b}{2a}).
Vertex Formula (Calculus)
f'(x) = 0
The vertex is a stationary point where the slope of the tangent line is zero. Fi...
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Challenging
Which of the following equations matches the key features of the worked example f(x) = 2x^2 - 8x + 6: an upward-opening parabola with vertex at (2, -2) and y-intercept at (0, 6)?
A.f(x) = 2(x-2)^2 - 2
B.f(x) = -2(x-2)^2 - 2
C.f(x) = 2(x+2)^2 - 2
D.f(x) = 2(x-2)^2 + 6
Challenging
A quadratic function has a vertex at (-1, 4) and x-intercepts at (1, 0) and (-3, 0). Which equation represents this function?
A.f(x) = (x-1)^2 + 4
B.f(x) = -(x+3)(x-1)
C.f(x) = -(x+1)^2 + 4
D.f(x) = (x+1)^2 + 4
Challenging
Use the first derivative to determine the vertex of f(x) = -0.5x^2 - 3x + 8, and then state the function's range.
A.Vertex at (3, -5.5); Range y ≥ -5.5
B.Vertex at (-3, 12.5); Range y ≤ 12.5
C.Vertex at (-3, 12.5); Range y ≥ 12.5
D.Vertex at (3, -5.5); Range y ≤ -5.5
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