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C1 sequences


Can somebody please check my answer, i don't think it is right. i'm really stuck please help
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TeeEm
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Original post by kandykissesxox
Can somebody please check my answer, i don't think it is right. i'm really stuck please help


where?
So the sum of an arithmetic series is (n/2)(2a + (n-1)d). You know that equals 25250, with d being 5.
Find n from there

...which you have, and...
Original post by shawn_o1
So the sum of an arithmetic series is (n/2)(2a + (n-1)d). You know that equals 25250, with d being 5.
Find n from there


yes, I'm sorry its upside down
you forgot to do the square root towards the end
Original post by the bear
you forgot to do the square root towards the end


Yes but it's non calc
It might be easier to complete the square with n^2 + n - 10100 = 0
Original post by kandykissesxox
Yes but it's non calc


you could have divided each term in the Quadratic by 5 :cool:
Original post by the bear
you could have divided each term in the Quadratic by 5 :cool:



Oh yeah!! i'll try that. thank you
ok i got an answer of : 0=(n+0.5) squared - 10100.25

so would the final answer be 101?
n+0.5 = 100.5 so...
Original post by shawn_o1
n+0.5 = 100.5 so...



oops :redface:
Original post by kandykissesxox
oops :redface:


i don't get how you solved that
ok final and is : 10099.75 please tell me this is right
You did fine up to the point where you tried to use the quadratic formula, I directed you to the easier method of completing the square, and yeah, the answer is 100. Check by substituting n =100, a = 5, d = 5 back in (n/2)(2a + (n-1)d) , see if you get 25250.
Original post by shawn_o1
You did fine up to the point where you tried to use the quadratic formula, I directed you to the easier method of completing the square, and yeah, the answer is 100. Check by substituting n =100, a = 5, d = 5 back in (n/2)(2a + (n-1)d) , see if you get 25250.


but i completed the square like you said:frown:

0=n squared + n-10100
=0(n+0.5)squared -0.25-10100
=0(n+5)squared-10100.25
so
10100.25-5=n
10099.75=n
Yeah, you forgot to square root 10100.25. An easy way to do it on a non-calculator paper is to multiply it by 4 (40401), you can easily find the square root of that (201), then divide that by 2.
Which leads back to the n+0.5=100.5 that I ended up with
Original post by kandykissesxox
but i completed the square like you said:frown:

0=n squared + n-10100
=0(n+0.5)squared -0.25-10100
=0(n+5)squared-10100.25
so
10100.25-5=n
10099.75=n


where did that go?
Original post by shawn_o1
Yeah, you forgot to square root 10100.25. An easy way to do it on a non-calculator paper is to multiply it by 4 (40401), you can easily find the square root of that (201), then divide that by 2.
Which leads back to the n+0.5=100.5 that I ended up with



i don't get why you square root?

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