Help arithmetic sequence

Help!! I’m stuck on the last part of part B I got
Sn = 300n (32-n)
But I don’t get how to get the maximum as 16, is this just trial and error??

(edited 1 year ago)

Original post by Alevelhelp.1

Help!! I’m stuck on the last part of part B I got
Sn = 300n (32-n)
But I don’t get how to get the maximum as 16, is this just trial and error??

S_n

is a quadratic in n. How do you find the maximum of a quadratic?

(edited 1 year ago)

Original post by ghostwalker

S_n

is a quadratic in n. How do you find the maximum of a quadratic?

Set Sn equal to zero, but I get 32 and 0 as answers

Original post by Alevelhelp.1

Set Sn equal to zero, but I get 32 and 0 as answers

They're not answers; they're the roots.

You should know that the max/min occurs at the midpoint of the two roots (if it has them) of a quadratic.

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