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Mathematics 9 Online
OpenStudy (anonymous):

can someone show me hot to evaluate this

OpenStudy (anonymous):

OpenStudy (amistre64):

its the sum of numbers generated from 0 to n-1

OpenStudy (anonymous):

why from zero, its from 1

OpenStudy (amistre64):

k=1; but the first term is 1-1 = 0

OpenStudy (anonymous):

so what is the process to evaluate this

OpenStudy (amistre64):

when k=n; you get the nth number as n-1

OpenStudy (amistre64):

what do you mean by "evaluate"? thats a pretty vague term

OpenStudy (anonymous):

how do i get the answer

OpenStudy (amistre64):

.... depends on what kind of an answer a person is looking for.

OpenStudy (anonymous):

i looking for this answer: (n^2-n)/(2)

OpenStudy (amistre64):

ok , a formula fir the sum ... thats better

OpenStudy (amistre64):

lets write out what we know about the series A = {0 + 1 + 2 +... + (n-3) + (n-2) + (n-1)} if we add this to itself we get: A = {0 + 1 + 2 +...+ (n-3) + (n-2) + (n-1)} + A = {{n-1) + (n-2) + (n-3)+...+ 2 + 1 + 0 } ------------------------------------------------- 2A = {(n-1) + (n-1) + (n-1) +...+ (n-1) + (n-1) + (n-1)} which reduces to: 2A = n(n-1) A = n(n-1)/2

OpenStudy (amistre64):

n(n-1) (n^2-n) ----- = ------- 2 2

OpenStudy (amistre64):

Does that make sense?

OpenStudy (anonymous):

sure does, but i found it a different way

OpenStudy (amistre64):

all roads lead to rome, except for the one on the left :)

OpenStudy (anonymous):

no, all roads dont lead to rome

OpenStudy (anonymous):

whoever told you that is wrong

OpenStudy (anonymous):

lets try this. the formula for \[\sum_{k=1}^n k = \frac{n(n+1)}{2}\] and \[\sum_{k=1}^n 1=n\] so you can compute \[\frac{n(n+1)}{2}-n\] for your answer

OpenStudy (anonymous):

right thank you, that was the way i did it too

OpenStudy (amistre64):

whew!! good thing sate came along and gave us the right way to do it ... ;)

OpenStudy (anonymous):

yeah, good thing you suck

OpenStudy (amistre64):

now that was uncalled for.

OpenStudy (anonymous):

no, your smart *** reply was uncalled for and you know it

OpenStudy (amistre64):

you appear to be misinterpreting my response ... but whatever, I gave sate props for his reply.

OpenStudy (anonymous):

yeah, yeah sure thats what you did

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