Find what i did was: i used to expand but the suggested answer is ........ where did i go wrong?
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The sum has n-3 terms, not n terms.
Originally Posted by red_dog The sum has n-3 terms, not n terms. then... =(1/2)(n-3)(n+6) ....i still don't get the (n+4)....@"@
Originally Posted by wintersoltice then... =(1/2)(n-3)(n+6) ....i still don't get the (n+4)....@"@
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