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Level 7-8 Algebra - Graphs 02
Graphs are useful for recording data.

Level 7-8 Algebra - Graphs 02

Straight-line graphs show patterns clearly. Learn gradient, intercepts, and coordinates to plot and read lines with confidence in KS3 Maths.

Fascinating Fact:

The equation y = 2x + 1 makes a straight line. The gradient 2 means the line rises 2 units for every 1 across.

In KS3 Maths, you use coordinates and equations to draw and interpret straight-line graphs. You’ll link tables to lines, find gradients and intercepts from y = mx + c, and solve real problems using graphs.

  • Gradient: How steep a line is; the change in y divided by the change in x.
  • y-intercept: The value of y where a line crosses the y-axis (when x = 0).
  • Coordinate pair: A point written as (x, y) that shows a position on a grid.
How do I find the gradient and intercept from y = mx + c?

In y = mx + c, the gradient is m and the y-intercept is c. For y = 2x + 1, gradient = 2 and intercept = 1.

How do you plot the line y = 2x + 1 in KS3?

Make a table (e.g., x=0,1,2), calculate y (1,3,5), plot the points (0,1), (1,3), (2,5), then join with a ruler and label axes.

What does a positive or negative gradient mean on a graph?

A positive gradient rises as x increases; a negative gradient falls. Zero gradient is a horizontal line; an undefined gradient is a vertical line.

1 .
Two coordinates of a line are as follows: (3, 21) and (2, 14). How might the line best be described?
It has a positive gradient
It has a negative gradient
It is horizontal
It is vertical
Lines that slope from the bottom left to the top right have a positive gradient. If you cannot imagine a line then plot it to see what it looks like
2 .
Which of these equations would give the steepest gradient?
y = x
y = x + 1
y = x + 2
All the above are the same gradient
If all the lines were plotted on the same graph they would run parallel to each other
3 .
What is the mid point of the line (1, 9) (5, 15)
(1, 15)
(3, 12)
(6, 24)
(9, 15)
Take the first number in the first bracket and add it to the first number in the second bracket and divide the answer by two - gives you 3. Then do the same for the second numbers in the brackets and you will get 12
4 .
If a graph equation contains only the signs of plus, minus and equals then what could you definitely say about the line?
It is very long
It is very short
It is straight
It is curved
These are the simplest equations to plot
5 .
If a graph equation contains an exponent then what could you definitely say about the line?
It is very long
It is very short
It is straight
It is curved
Remember an exponent is the small number to the upper-right of another number. As soon as you see one of these in an equation you should expect a curve
6 .
Which of these graphs would give you the most shallow gradient?
y = 3x - 1
y = 4x - 1
y = 5x - 1
y = 6x -1
The more times you multiply x, the steeper the gradient becomes
7 .
Which of these equations would give the steepest gradient?
y = x
y = 2x
y = 3x
y = 4x
In the correct answer, each movement of a unit along the x axis means a movement of 4 units up the y axis
8 .
Two coordinates of a line are as follows: (3, 12) and (2, 8). What is the equation?
y = 2x
y = 4x
y = 6x
y = 8x
If you plot the coordinates you will see that for every unit moved along the x axis, you move 4 units up the y axis. Working out an equation in this way has the grand name of the 'gradient-intercept' method
9 .
Two coordinates of a line are as follows: (2, 15) and (6, 10). How might the line best be described?
It has a positive gradient
It has a negative gradient
It is horizontal
It is vertical
It is worth remembering that you can have both positive and negative gradients in ANY quadrant
10 .
On a distance-time graph what does a line segment that is horizontal tell you?
The data is incorrect
The distance travelled was slowing down
The distance travelled was speeding up
There was no movement during the period
The line on the time axis continues but on the distance axis it has paused
You can find more about this topic by visiting BBC Bitesize - Graphs

Author:  Frank Evans (Specialist 11 Plus Teacher and Tutor)

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