
Answer is

When it's powered numbers, remember to choose the one with the largest power. For example,

And

Choose 10, same goes to y, where you choose 7 not 4 since 7 is larger.
Hope this helps. - M
As you increase the subintervals the area will be closer and closer to the real value. In other words your approximation gets better.
As you increase the intervals, there will be more rectanagles and the added area of these rectangles are converging towards the actual area under the curve.
The answer is f(x)=x²+2x when evaluated with -3 gives you the value of 3
It would be
(X^4+2X^2) -119(X^2-2X) then you would simplify
X^4+2X^2-119X^2-2X
So it would be
X^4+117X^2-2X=0
So basically X is undefined