cp1 series question

[regal raft]

The sum of cubes of the first n +ve odd numbers is n^2(2n^-1)

The sum of the cubes of 10 consecutive +ve odd numbers is 99800

Find the smallest of these 10 consecutive positive odd numbers

helpppp pls

<@&791435371564892232>

[merry kiln]

@regal raft send an image of the question

[regal raft]

kl

part b

[merry kiln]

Yeh so 99800 = (2n^2 -1)n^2
let u = n^2 then take everything to RHS

solve quadratic in terms of u and then find n

[regal raft]

is the substiution necessary

i did this already without the sub and got some mad decimals

yh i got decimals again

@merry kiln

[merry kiln]

use summation formula

I think

$\sum_{r=n}^{n+9} (2r-1)^3$

[delicate junco]

david

[regal raft]

tried that as well 😭

[merry kiln]

Hmmm what did you get

[regal raft]

imaginary numbers

[merry kiln]

😭 whattt

[regal raft]

idfk this question is cursed

[regal raft]

ill try this again

[merry kiln]

Remember to subtract the sum from 1 to n-1

[regal raft]

oh yhhh

i just subbed in n+9 and n then subtracted

so dumb

i got it

tysm