The nth term of the given by (-1)n2.2n-1 find the product of the fifth and sixth term

Answer 1

I can't make out your formula.
If it's a_n = (-1)^(n^2) * 2n - 1
then you have
((-1)^25*10-1)*((-1)^36*12-1) = (-10-1)(12-1) = -121

If that's not right, then fix it with some parentheses, and follow the same steps. Post your work if you get stuck. Just replace each n by 5 or 6 in your calculations.