Multiplication Observations and Ideas

R-11 Multiplication Generalizations 


edge x edge= array

Red (-) x Red (-)= Black (+)  Double flip

Black (+) x Black (+)= Black (+)  No Flips at all

Black (+) x Red (-) = (-) You only flip it once to red or negative

Red (-) x (+) = Red (-)You only flip once to red or negative

Multiplication arrays

The net value is 12.

The net value is 6. The red column and the black next to it zeroate.

 

The net value is -4. The bottom black row and red row next to is zeroates. 

** Students were given a chart of multiplication arrays and built them. 

* Black edge: row or column not flipped

*Red edge: row or column flipped

*2 reds: need to flip twice=black

R-7 Every Subtraction problem can be rewritten as an addition problem

R-7 Every Subtraction problem can be rewritten as an addition problem

Is this true or false?

 Can you give examples?

1st idea
7-3=4
2+2=4

2nd idea
3-8=-5
3+8=11

3rd idea
3+4=7 Fact families
7-4=3

4th idea
7+(-3)=4    Using same numbers , but changing the sign of the second one.

How can you rewrite -4-(-4) as an addition problem?

Homework: Write 4 problems that prove each subtraction rule.
Comp. Q corrections due Wed 1/14

R-6 Our final Rules for negatives

(+)-(+) and (-)-(-)

Find the absolute value of the two numbers. If the first number is larger, the answer is positive. If the 1st number is smaller, answer is negative.

(+)- (-) and (-) - (+)

Add the absolute values, if the first number is negative the answer is negative. If the first number is positive the answer is positive.

Write 4 problems that prove each subtraction rule.

Posters- 2 Subtraction rules