Linear Graphs
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Coordinates
- The Cartesian plane has a horizontal x-axis and vertical y-axis meeting at the origin (0,0).
- Coordinates are written as (x, y) – x units horizontally, y units vertically.
- Positive x: right of origin; negative x: left. Positive y: above; negative y: below.
- Example: (2,5) is 2 right, 5 up; (-1,-4) is 1 left, 4 down.
- Check the scale on axes – 1 square may not equal 1 unit.
Points on the Cartesian plane
Gradient of a Line
- Gradient measures steepness: for 1 unit right, go up (positive) or down (negative) by the gradient.
- Gradient = change in y / change in x = rise/run.
- Find gradient by drawing a right-angled triangle between two points on the line.
- Uphill lines have positive gradient; downhill lines have negative gradient.
- Formula: gradient m = (y₂ - y₁) / (x₂ - x₁).
- To draw a gradient of a/b: move b units right, a units up (positive) or down (negative).
Gradient of a line: rise/run construction

Equations of Straight Lines (y = mx + c)
- General equation: y = mx + c, where m is gradient and c is y-intercept.
- y-intercept is where the line crosses the y-axis (x=0).
- To find equation from graph: find gradient m (rise/run), read y-intercept c, substitute into y = mx + c.
- If y-intercept not visible, substitute a point (x,y) into y = mx + c to solve for c.
- Horizontal line: y = c (gradient 0). Vertical line: x = k (gradient undefined).
y = mx + c
Drawing Straight Line Graphs
- Use a table of values – choose at least 3 x-values, compute y, plot points, join with a straight line.
- Alternatively, start at y-intercept c, then move 1 unit right and m units up (or down if negative).
- For fractional gradient a/b, move b units right and a units up/down.
- Always plot at least 3 points to check for errors.
Plotting from a table of values
Parallel Lines
- Parallel lines have the same gradient but different y-intercepts.
- They never intersect.
- To find equation of a line parallel to y = mx + c through (x₁,y₁): use y = mx + d, substitute point to find d.
Parallel lines
Slide
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Câu hỏi luyện tập
Xem trước miễn phí — 8 trên 51 câu hỏi. Đăng ký để xem tất cả.
1.What is the gradient of the line y = 2x - 3?
Easy- A-3
- B2
- C3
- D-2
2.What is the y-intercept of the line y = 4x - 6?
Easy- A-4
- B4
- C6
- D-6
3.A line has gradient 3 and passes through (0, 1). What is its equation?
Easy- Ay = x + 3
- By = 3x + 1
- Cy = -3x + 1
- Dy = 3x - 1
4.What is the gradient of a horizontal line?
Easy- Aundefined
- B-1
- C0
- D1
5.What are the coordinates of the origin?
Easy- A(1, 1)
- B(0, 1)
- C(1, 0)
- D(0, 0)
6.Find the gradient of the line passing through (1, 2) and (3, 6).
Easy- A4
- B1/2
- C3
- D2
7.What is the equation of the line parallel to y = 5x + 6 that passes through (0, -7)?
Easy- Ay = 5x + 6
- By = -5x - 7
- Cy = 5x + 7
- Dy = 5x - 7
8.A line has gradient -2 and passes through (0, 4). What is its equation?
Easy- Ay = -2x - 4
- By = -2x + 4
- Cy = 2x + 4
- Dy = 2x - 4
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