Square difference calculation 1、10.3*9.7 2. 1 and 3 / 13 * 10 / 13 How about this?

Square difference calculation 1、10.3*9.7 2. 1 and 3 / 13 * 10 / 13 How about this?

10.3*9.7
=(10+0.3)*(10-0.3)
=100-0.09
=99.91
2)
16/13*10/13
=(1+3/13)*(1-3/13)
=1-9/169
=160/169

Calculation of square difference
19 and 7 / 9 times 20 and 2 / 9. Use the square difference formula to calculate the following for me,

The original formula = (20-2 / 9) (20 + 2 / 9) = 400-4 / 81 = 77 of 399 and 81

How to calculate the square difference

There is such a formula, (a + b) (a-b) = A & # 178; - B & # 178;
If you don't understand, ask a specific question, which you can't write at all

How to calculate square difference with computer
The model is fx-500es
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Press mode (setup)
Press 2 to choose 2: stat
Press 1
Enter the number and press=
Repeat input until it is finished
Then press AC to clear the screen (the data is still in memory)
Then press shift and 1 (STAT)
Press 5 to choose 5: VAR
Press 3 to choose 3: x6n
Press=
This is the standard deviation, and the square is the variance