SOLUTION: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 .... .... .... .... .... ..... a) what's the 3rd number from left in 10th row? b) wha

Question 979025: 1
2 3
4 5 6
7 8 9 10
11 12 13 14 15
.... .... .... .... .... .....
a) what's the 3rd number from left in 10th row?
b) what's the position of 2009?
Answer by KMST(5328) (Show Source): You can put this solution on YOUR website!
Each row has one more number than the row above.
It is what math teachers call an arithmetic sequence, or an arithmetic progression.
(It depends on where you go to school).
Row has numbers,
and rows through contain a total of
numbers.
That means that the last number on row is .
The last number on row is ,
and the third number in row is .
If we say that number 2009 is in row ,
the last number on row is

There is more than one way to solve that inequality.
You could find the solutions to the quadratic equation
<-->
as ,
and realize that the solution to <--->
.
So marks the row above number .
The last number on row is ,
and you need to go numbers further,
on row to get to .
So, is the number on row .
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