SOLUTION: There are 8436 steel balls, each with a radius of 1 centimeter, stacked in a pile, with 1 ball on top,3 balls in the second layer, 6 in the third layer, 10 in the fourth, and so on

Question 898128: There are 8436 steel balls, each with a radius of 1 centimeter, stacked in a pile, with 1 ball on top,3 balls in the second layer, 6 in the third layer, 10 in the fourth, and so on. The number of horizontal layers in the pile is..?
Answer by josgarithmetic(39618) (Show Source): You can put this solution on YOUR website!
Layer Number__________Balls in Layer
1_______________________1
2_______________________3
3_______________________6
4______________________10
5______________________15__________added 5
6______________________21__________added 6
.
.
n__________________sum of 1 to n, the number of balls in a layer.

, the number of balls in the layer at index n.

The formula for this kind of summation is for the SEQUENCE on which the summation is based.

.
Solve for n, which is also the number of horizontal layers.
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