Create sum expression from algebraic expression

Oct 2009
5,577
2,017
but are the calculations correct?
No.

900: 1x+2x+3x+4x+5x+6x+6x+6x+6x+6x+6x+6x
...
900: S (upper: 5 lower: 1) ix + S (upper:6 lower: 1) 6x where x = 10000
In the explicit sum, 6x occurs 7 times, but in the sigma-expression, it is used only 6 times.

500: 1x+2x+3x+4x+5x+6x+7x+8x+8x+8x+8x+8x
...
500: S (upper: 5 lower: 7) ix + S (upper:5 lower: 1) 6x where x = 10000
It is not clear what 6x is doing in the sigma-expression and why you have \(\displaystyle \sum_{i=7}^5ix\), where the upper limit is less than the lower one.
 
Dec 2011
22
0
ok is this statement true?

\(\displaystyle \sum_{i=1}^6ix\)+\(\displaystyle \sum_{i=1}^58x\) = 680000
 
Last edited:
Oct 2009
5,577
2,017
\(\displaystyle \sum_{i=1}^6ix+\sum_{i=1}^58x=\left(\sum_{i=1}^6i+\sum_{i=1}^58\right)x=(21+40)x=61x\). However, in [post=707449]post #8[/post] the expression labeled 500 has \(\displaystyle 1x+2x+3x+4x+5x+6x+7x+8x+8x+8x+8x+8x\) = \(\displaystyle \sum_{i=1}^7ix+\sum_{i=1}^58x = 28x+40x = 68x\), which is indeed 680000 for x = 10000.
 
Dec 2011
22
0
Oh ok I see my mistake now, I was confused on the use of the subscripts. Now I understand how to write them correctly. Thank you very much, I really appreciate it.
 
Dec 2011
22
0
how come I cannot set the upper script 12?

\(\displaystyle \sum_{i=1}^{12}80000x=960,000\)
 
Last edited:
Oct 2009
5,577
2,017
You need to wrap the upper limit {12} in curly braces in LaTeX.

Again, this is not an equation, so I can't say if it true or false. This thread is becoming big, and I am having trouble getting your implied references to earlier posts.