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April 19, 2015

April 19, 2015

Posted by **Arnau** on Tuesday, April 30, 2013 at 1:28am.

- Math (Algebra) -
**Safwan**, Tuesday, April 30, 2013 at 7:13am160

- Math (Algebra) -
**Reiny**, Tuesday, April 30, 2013 at 8:08amfrom (0,10) to (0,-10) -- 21

from (1,9) to (1,-9) --- 19

from (2,8) to (2,-8) --- 17

..

from (9,1) to (9,-1) -- 3

and (10,0) ----- 1

same thing on the left side, but we can't count the centre line twice, so

sum = 2(1+3+5+...19) + 21

there are 10 terms in the series

sum = 2(5)(first + last) + 21

= 10(20) + 21 = 221

or 2(1+3+5+..+21) - 21

= 2(11/2)(1 + 21) - 21 = 221

There are 221 such ordered pairs.