Question

Uhhh... Help?

Answer 1

How come \[\Large \int\limits_1^3 2x dx = x^2|_1^3=3^2-1^2=8 \\ \Large \int\limits_3^1 2x dx = x^2|_3^1=1^2-3^2=-8\] Then what if you do this: \[\Large \sum_{n=1}^3 2n = 2*1+2*2+2*3=12 \\ \Large \sum_{n=3}^12n=-12?\]

Answer 2

case one :-
we are constructing an integral bounded by 1 and 3