Question

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I need help number 11 please!

Answer 1

I am assuming you know that the summation of k is represented by k(k+1)/2, assuming k starts at 1 and ends at k.

Therefore an intuitive way of evaluating the given summation is to think of it as two summations: In the form (14-2k) summed from 1 to 15 and then subtract (14-2k) summed from 1 to 2 to give the wanted summation.

and using this intuition we find it is equivalent to [14(15)-2(15)(16)/2-14(2)+2(2)(3)/2]

Answer 2

Which is -52