Further Graphs
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Types of Graphs
- Straight lines: y = mx + c (e.g., y = 3x + 2). Key lines: y = x and y = -x.
- Horizontal lines: y = c (e.g., y = 4).
- Vertical lines: x = k (e.g., x = 2).
- Quadratic graphs: y = ax² + bx + c. Shape is a parabola: u-shaped (positive a) or n-shaped (negative a).
- Reciprocal graphs: y = a/x. Two L-shaped branches; x ≠ 0. Positive a gives branches in first and third quadrants.
Positive and negative quadratics
Key Features of Quadratic Graphs
- The turning point is called the vertex: minimum for positive quadratics, maximum for negative quadratics.
- Quadratic graphs have a vertical line of symmetry through the vertex: x = k (k is x-coordinate of vertex).
- Roots are x-intercepts where y = 0. A quadratic can have 0, 1 (touches), or 2 roots.
- Roots are symmetric about the line of symmetry.
- Quadratic graphs always have one y-intercept (where x = 0).
Key features of a quadratic graph
Drawing Graphs from Tables
- Substitute x-values into the equation to find y-values. Use brackets for negative x and follow BIDMAS.
- For reciprocal graphs, do not include x = 0 (division by zero).
- Plot points accurately (within half a square). Join with a smooth freehand curve (no ruler).
- Use calculator table function: enter function, start/end x, step size. Check given y-values.
- If a point doesn't fit the curve shape, check your working.
Solving Equations from Graphs
- To solve f(x) = 0, read the x-intercepts (roots) of the graph of y = f(x).
- To solve f(x) = k, draw horizontal line y = k and read x-coordinates of intersections.
- To solve f(x) = g(x), plot y = f(x) and y = g(x); solutions are x-coordinates of intersection points.
- For equations not in the form 'graph = ...', rearrange to match the given graph. E.g., x² - 4x + 3 = 1 becomes x² - 4x - 2 = -4.
- When solving for x, give only x-coordinates. Include y-coordinates only for simultaneous equations.
Solving f(x) = g(x) graphically
Example: Quadratic Graph from Table
- Substitute each x-value into y = x² − 4x − 3 to complete the table of values: | x | −2 | −1 | 0 | 1 | 2 | 3 | 4 | 5 | |---|---|---|---|---|---|---|---|---| | y | 9 | 2 | −3 | −6 | −7 | −6 | −3 | 2 |
- Plot the points and draw a smooth u-shaped curve for −2 ≤ x ≤ 5.
- Solve x² − 4x − 3 = 0 by reading the x-intercepts from the graph: x ≈ −0.65 and x ≈ 4.65.
- Line of symmetry: x = 2, the midpoint of the roots (and −b/(2a) = 4/2 = 2).
y = x² − 4x − 3
Example: Reciprocal Graph
- Substitute each x-value into y = 15/x to complete the table of values: | x | −5 | −3 | −2 | −1 | 1 | 2 | 3 | 5 | |---|---|---|---|---|---|---|---|---| | y | −3 | −5 | −7.5 | −15 | 15 | 7.5 | 5 | 3 |
- Draw two separate branches, one for x < 0 and one for x > 0; do not connect them at x = 0.
- Solve 15/x = 6 by drawing the horizontal line y = 6 and reading the x-coordinate of the intersection: x = 2.5.
- Reciprocal graphs have asymptotes at x = 0 and y = 0.
y = 15/x
Example: Solving with Horizontal Line
- Substitute each x-value into y = 1 + 5x − x² to complete the table of values: | x | −1 | 0 | 1 | 2 | 3 | 4 | 5 | |---|---|---|---|---|---|---|---| | y | −5 | 1 | 5 | 7 | 7 | 5 | 1 |
- Draw the horizontal line y = 3. The x-coordinates of the intersections solve 1 + 5x − x² = 3.
- Solutions: approximately x = 0.44 and x = 4.56.
- Line of symmetry: x = 2.5 (the midpoint of the two solutions above, and the x-coordinate of the vertex).
y = 1 + 5x − x²
Example: Solving with Another Line
- Substitute each x-value into y = −x² + x + 5 to complete the table of values: | x | −3 | −2 | −1 | 0 | 1 | 2 | 3 | 4 | |---|---|---|---|---|---|---|---|---| | y | −7 | −1 | 3 | 5 | 5 | 3 | −1 | −7 |
- Draw the line y = x. The x-coordinates of the intersections solve −x² + x + 5 = x, which simplifies to x² = 5.
- Solutions: x = ±√5 ≈ ±2.24.
- Vertex (turning point): (0.5, 5.25). Line of symmetry: x = 0.5.
- Roots of −x² + x + 5 = 0: approximately x = −1.79 and x = 2.79.
y = −x² + x + 5
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Soal latihan
Pratinjau gratis — 8 dari 57 soal. Daftar untuk melihat semuanya.
1.Which of the following is the equation of a straight line?
Easy- Ay = 3x + 2
- By = x2 + 3x + 2
- Cy = 1/x
- Dy = -x2 + 3x + 2
2.What is the name of the shape of a quadratic graph?
Easy- AParabola
- BHyperbola
- CStraight line
- DCircle
3.For a quadratic graph y = ax2 + bx + c, if a is positive, the graph is:
Easy- Au-shaped
- Bn-shaped
- Ca straight line
- DL-shaped
4.What is the equation of the line of symmetry for a quadratic graph with vertex at (2, 5)?
Easy- Ax = 2
- By = 2
- Cx = 5
- Dy = 5
5.Which of the following is a reciprocal graph?
Easy- Ay = 4/x
- By = 4x + 1
- Cy = x2 - 4
- Dy = -x2 + 4
6.What is the value of y when x = -2 in the equation y = x2 - 3x?
Easy- A10
- B-2
- C-10
- D2
7.Which of the following is the equation of a horizontal line?
Easy- Ay = 4
- Bx = 4
- Cy = x
- Dy = -x
8.The graph of y = -x2 + 2x + 3 is:
Easy- An-shaped
- Bu-shaped
- Ca straight line
- DL-shaped
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