81
18
27
9
45
2007-01-20 21:52:57 · 34 answers · asked by Anonymous in Science & Mathematics ➔ Mathematics
let y=10,x=1
10-1=9=y-x
9^2=(y-x)^2
=y^2+x^2-2yx
=10^2+1^2-2*10*1
=100+1-20
=101-20=81
therefore,9^2=81
think of this as a
chequered table with
10X10 squares in it
you want the value of 9X9
squares-take away one
row and and one column
from it
so far we have (10x10)-(2x10)
=80
look at this carefully-we have have only
taken away 19 (instead of 20) because
we have counted the overlapping
square twice,so we add one back
now we have
(10x10)-(2x10)+1
=100-20+1
=80+1
=81
don't just learn a 'times table'-
ask why? as well
i hope that this helps
2007-01-20 22:05:35 · answer #1 · answered by Anonymous · 1⤊ 0⤋
9 times 9 = 9² = 81
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2007-01-21 01:34:23 · answer #2 · answered by aeiou 7 · 0⤊ 0⤋
9*9=81
2007-01-21 00:20:54 · answer #3 · answered by santmann2002 7 · 0⤊ 0⤋
9 times 9 = 9*9 =81
2 times 9 = 2*9 = 18
3 times 9 = 3*9 = 27
1 times 9 = 1*9 =9
5 times 9 = 5*9 = 45
Hopefully this will help
2007-01-24 11:56:44 · answer #4 · answered by LYNDA M 5 · 0⤊ 0⤋
81
2007-01-24 02:24:47 · answer #5 · answered by Emma C 4 · 0⤊ 0⤋
81
2007-01-21 05:34:31 · answer #6 · answered by johanna c 2 · 0⤊ 0⤋
81
2007-01-20 22:22:47 · answer #7 · answered by tribalgirlie 2 · 0⤊ 0⤋
81
2007-01-20 22:21:52 · answer #8 · answered by cookie monster 1 · 0⤊ 0⤋
81
2007-01-20 22:12:09 · answer #9 · answered by Anonymous · 0⤊ 0⤋
81
2007-01-20 22:10:50 · answer #10 · answered by Lucia O 1 · 0⤊ 0⤋
81
2007-01-20 22:02:24 · answer #11 · answered by Anonymous · 0⤊ 0⤋