2TH/vwo §1.4 Directly proportional

• Wiskunde
• Middelbare school
• havo, vwo
• Leerjaar 2

§1.4 Directly proportional

This title probably doesn't mean a thing to you.

After this lesson it will!

Question:

For which graph(s) is the following statement true:

If x is made twice as large, then also y becomes twice as large.

This rings true for graph ...

1. 2
2. neither of them
3. 1
4. both of them

If x is made twice as large, then also y becomes twice as large.

This is true for graph 1 only, because:

on graph 1 there are points (2, 5) and (4, 10) to be found.

Multiplying x :            2 by 2 gives 4   and 

multiplying y :           5 by 2 gives 10.

In the next slide we come back at this with the Theory from the book.

What is the dutch expression for 'directly proportional'?

Directly proportional is in dutch:

recht evenredig

Question:

Which statement is true:

1. If a formula is linear, it is also a directly proportional relation.

2. If a formula is  directly proportional,  then the graph is linear.

Answer this in the next slide!

Which statement is true?

1. 1
2. neither
3. both
4. 2

Solution:

Which statement is true:

1. If a formula is linear it is also directly proportional.

2. If a formula is directly proportional it is also linear.

Statement 2 is true. Number 1 is not, because a linear graph doesn't have to go through the origin. A linear graph is a straight line. No more.

Homework

As usual, choose the right path:

+  havo:   support path

+  vwo:    standard path or challenge path,

                  You may SKIP:   24 and 30