Thursday

January 29, 2015

January 29, 2015

Posted by **Daniel** on Monday, October 9, 2006 at 10:43pm.

1st 2nd 3rd 4th

. . . .

. . . . . . . . . . . .

. . . .

Is there a simple formula for this?

0, 1, 3, 6, 10, 15, 21, 28, 36, 45, 55, 66, 78, 91, 105, 120, 136, 153, 171, 190, 210, 231, 253, 276, 300, 325, 351, 378, 406, 435, 465, 496, 528, 561, 595, 630, 666, 703, 741, 780, 820, 861, 903, 946, 990, 1035, 1081, 1128, 1176, 1225, 1275, 1326, 1378, 1431

Search on Trianglular numbers on Google.

[k(k+1)]/2 is the general formula.

k=1 gives (1*2)/2=1

k=2 gives (2*3)/2=3

k=10 (10*11)/2 = something you can do.

k=20 (20*21)/2 = something you can do.

k=100 (100*101)/2 = something you can do.

Prove the formula by induction.

HELP MATH

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