**Proportion Graphs**

Starter

y is proportional to x. When y = 7, x = 2. Find the relationship between y and x as an algebraic formula.

How does your formula compare to the formula y = mx + c ?

What does this tell you about the graph of a proportional relationship?

Proportion, graphs and gradient.

The gradient of a proportion graph is equal to the value of the constant of proportionality ('k').

This represents the rate of change of the situation (i.e. how much one variable changes for a unit change in the other).

Proportion Graphs

**L.O. - Understand the commonality in the graphs and proportional relationships, and use such graphs.**

Starter

y is proportional to x. When y = 7, x = 2. Find the relationship between y and x as an algebraic formula.

y = 3 x

How does your formula compare to the formula y = mx + c ?

It is the same formula, with m = 3 , and c = 0.

What does this tell you about the graph of a proportional relationship?

That the graphs of all proportional relationships are straight lines passing through the origin.

1

2

1

2

There are 16 oz in every lb. Draw the graph of oz against lb for values up to 6 lb.

Proportion Graphs

There are 16 oz in every lb. Draw the graph of oz against lb for values up to 6 lb.

Proportion graphs

The graph of a proportional relationship will always pass through the point (0, 0).

If the proportion is directly between two variables, the graph will always be a straight line.

Example

What is the relationship between Force and Pressure?

Example

What is the relationship between Force and Pressure?

P = F

OR

F = 5P

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5

Activity

Complete the proportion graph worksheet

Activity

Complete the proportion graph worksheet

Proportional, non, non, non (or proportional to the cube), Proportional, non.

1a. y = 3x, 30 b. y = 4x, 25 c. y = 0.5x, 5

d. y = 1.2x, 0.5

2) k = 100, y = 100x

5, 20, 45, 80, 125

No constant of proportionality, goes up by different amount every time.

Area is proportional, with P = A

1

20

Plenary

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