Example 7 (iv): Was there any usage of the Sum To n formula for AP? If not, how did they work it out?
I initially used the Sum To n formula for AP, taking n = (n(n+1))/2 , a = (n^2 - n + 2)/2 , d = 1 .
However, this got me an equation with n^4 which is not ideal considering that the question required an equation only up to n^3.
This is what i ended up with: (n/2) * (n+1) * [ (n^2)/4 - n/4 - 1/2 ] , no where near the required equation.
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I initially used the Sum To n formula for AP, taking n = (n(n+1))/2 , a = (n^2 - n + 2)/2 , d = 1 .
However, this got me an equation with n^4 which is not ideal considering that the question required an equation only up to n^3.
This is what i ended up with: (n/2) * (n+1) * [ (n^2)/4 - n/4 - 1/2 ] , no where near the required equation.
(Click thumbnail to view larger image)
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