1TTO§8.3 Subtracting negative numbers 23-24 PTI

• Wiskunde
• Middelbare school
• havo, vwo
• Leerjaar 1

QUESTION FOR YOU:

WHAT IS THE KEY WORD IN THE LAST SENTENCE ?

In other words: what's NEW ?

SOLUTION:

THE KEY WORD IS:       REMOVING!

In §8.2 the witch only ADDED hot and cold blocks, 

but in §8.3 she TAKES OUT hot and cold blocks!

Let's PRACTICE this some times.

+ first your teacher gives an example,

+ then you get a little time to think about the next one

+ finally one of you gets the turn to speak up

+ SAFETY WARNING: taking out blocks is more difficult than putting in!

In the same way we tackle 19 now.

+ now however a CALCULATION is asked, too

+ for example:  

  6 - -5 = ...          A double minus?! Yes! The first minus is the command 'TAKING OUT' 

 and the second minus is of a COLD BLOCK. 

So we get this:

                                       1 - 4 = -3

In fact        --        can be written as          +            !

So we get this:

                                       5 -- 2 = 5 + 2 = 7

Finally a task for you!                   

5 - ..... = -3

1. -8
2. 2
3. 8
4. -2

5 -   .... = -3

Start number is  5

The result is  -3

So we subtract 8.  That's the number that has to be filled in on the dots!

In whitches' words: The temperature in the kettle is 5 degrees.

To get -3 as new temperature she TAKES OUT 8 HOT BLOCKS.

ATTENTION: the next task isn't as easy as it may look!            

The answer is...

With arrows (=pijlen) on a number line once more!

We have to cover the distance from 2      to      -3

That distance is 5

However, we move TO THE LEFT on the number line and that means subtracting!

So the answer is:    5           Do you see how tricky this business is?!

​3​​1​​

​3​​1​​

​3​​2​​

​3​​2​​

Once more, we move TO THE LEFT on the number line and that means subtracting!

The complete calculation becomes:

2       -    5          =     -3  

​3​​1​​

​3​​1​​

​3​​2​​

Find the outcome for this task.

Someone will get the turn.

Find the outcome for second task.

Someone will get the turn.

Find the outcome for third task.

Key in your outcome!

 

My outcome is:

Solutions:

Finally one more with ADDING:

8.5 + ... = - 2.5

1. 11
2. -10
3. -11
4. -6

Going from +8.5  to  -2.5  means going 8.5 + 2.5 to the left.

So:

8.5  +  -11  =  -2.5                 '-11'  has to be filled in.

Homework time

Now do §8.3