# Thread: Help with Trapezoidal Area

1. ## Help with Trapezoidal Area

Find the trapezoid sum for .

There's the problem I'm having, I keep trying to do it and I get really huge numbers and then get stuck. Can someone help get me started on it so I can see how you did it and if I'm not starting it off wrong I'll elaborate on what I keep doing.

2. Originally Posted by Eternal Calculus Student
Find the trapezoid sum for .

There's the problem I'm having, I keep trying to do it and I get really huge numbers and then get stuck. Can someone help get me started on it so I can see how you did it and if I'm not starting it off wrong I'll elaborate on what I keep doing.
It always helps to draw it out if you are in doubt.
So sketch the function and draw the corresponding trapeziums.

I assume by $\displaystyle n = 2$, you mean that you want 2 subdivisions.

Since the horizontal distance is $\displaystyle 2$ units, then each subdivision will have horizontal distance of $\displaystyle 1$ unit.

This is the same as the height of the trapezium.

Now for the parallel sides of the trapezium, you will need to evaluate $\displaystyle f(2), f(3)$ and $\displaystyle f(4)$.

Can you go from here?

3. ## Given Formula

The general summation formula for the trapezoid sum is:
, where for all i

This is the formula they give for working a trapezoidal sum, I understand how to read the problem its just every time I try to use their formula I get a different answer than any of the answers I'm left to choose from.

4. Originally Posted by Eternal Calculus Student
The general summation formula for the trapezoid sum is:
, where for all i

This is the formula they give for working a trapezoidal sum, I understand how to read the problem its just every time I try to use their formula I get a different answer than any of the answers I'm left to choose from.
Read my response properly. I am giving you the "analytical version" of that formula.

Try to work out all the dimensions of the trapeziums, work out their areas, then add them together.

5. I realize what I was doing wrong, I was only halfing the first trapezium DX thank you for spelling it out for me! This really makes it a whole lot simpler for me haha