given the quadratic equation -2, 0, 3, 7 ...
Determine the expression of the nth term of this sequence
Which term of the sequence will be equal to 322?
the 1st differences are 2,3,4,...
so the nth term of the sum is
-2 + ∑(k=1,n-1) k+1 = -3+∑(k=0,n+1) k
Now we know that ∑(k=0,n+1) k = (n+1)(n+2)/2
so a_n = -3 + (n+1)(n+2)/2 = (n-1)(n+4)/2
which term is 322? n=24