why is it wrong?

Question

why is it wrong?

anonymous · Answer

attachment

amistre64 · Answer

well, if we want to use fomulas, we would have to expand it and work the terms

amistre64 · Answer

otherwise:

1(0^2) + 2(1^2) + 3(2^2)+ ... + 23(22^2)

seems like a bit much to brute math out

amistre64 · Answer

i(i^2+1-2i)

i^3+i-2i^2

$$\sum i^3+\sum i-2\sum i^2$$

anonymous · Answer

i did it the long way and added it lol

anonymous · Answer

okay..

anonymous · Answer

whats the shortcut
how do u get your answer

amistre64 · Answer

we, i know the formulas for i and i^2 ... i^3 would either have to be looked up or reinvented

amistre64 · Answer

i(i-1)^2 = i(i^2+1-2i) = i^2 + i - 2i

by exanding it into a poly, we can play with it term for term

anonymous · Answer

okay polynomial expansion then?

amistre64 · Answer

yep:  keep in mind that
$$\sum(a+b)=\sum a+\sum b$$
so if we can expand it into a polynomial, we can assess it term for term

anonymous · Answer

okay yes, i will

perl · Answer

this is a nice resource for summation powers http://www.math.com/tables/expansion/power.htm note that they use k instead of i

amistre64 · Answer

$$\sum_{a}^{b} i=\frac{n}{2}(b+a)$$
i^2 tho ...

1 + 4 + 9 + 16
   3     5    7
       2     2

1n + 3n(n-1)/2 + 2n(n-1)(n-2)/6 

n(2n^2+3n+1)/6

amistre64 · Answer

remembering the formulas is much simpler than trying to reconstruct them lol

anonymous · Answer

it easier then addition over and over again! thank you i got it:D

amistre64 · Answer

good luck ;)

anonymous · Answer

thank you so much:D