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(**) Squaring A Number Ending In 7:
A. This method comes from
algebra:
(10a – 3)2
= 100(a)(a - 1) + 10(4a) + 9
B. Using numbers instead of
variables we get the following:
1.
Write down 9.
2.
Add 1 to the ten’s digit and multiply by 4.
Write this number down, carry if necessary.
3.
Multiply the number in the ten’s digit by that number plus 1.
Write this result.
Ex [1] 372 =_________.
a)
Write down 9.
b)
4 x (3 + 1) = 16. Write 6,
carry *1.
c)
3 x (3 + 1) = 12 + *1 = 13. Write
13.
d)
The answer is 1369.
Ex [2] 872 =_________.
a)
Write down 9.
b)
4 x (8 + 1) = 36. Write 6,
carry *3.
c)
8 x (8 + 1) = 72 + *3 = 75. Write
75.
d)
The answer is 7569.
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