# Help with left hand Riemann sum?

• Apr 17th 2014, 01:53 PM
canyouhelp
Help with left hand Riemann sum?
I have this Riemann sum question: Attachment 30701and I thought I knew how to do the left hand riemann sum but now I'm unsure. Basically I've used it before but when I try to with these points I'm just getting really confused because they're all under the x-axis. I had to kind of do it upside down. My answer was -13.5 but I wasn't sure if I should make it 13.5 because it's the area? Also, can you check to see if I did the math right for it? 13.5 negative or positive could be wrong :/ Thanks!
• Apr 17th 2014, 02:09 PM
SlipEternal
Re: Help with left hand Riemann sum?
It is asking you to calculate the Riemann sum. It is not asking you to calculate the area. The Riemann sum calculates the area under the curve. Area above the curve could be considered "negative" area. In other words, -13.5 is correct.
• Apr 17th 2014, 02:18 PM
canyouhelp
Re: Help with left hand Riemann sum?
Quote:

Originally Posted by SlipEternal
It is asking you to calculate the Riemann sum. It is not asking you to calculate the area. The Riemann sum calculates the area under the curve. Area above the curve could be considered "negative" area. In other words, -13.5 is correct.

Okay, thanks!
• Apr 17th 2014, 02:25 PM
SlipEternal
Re: Help with left hand Riemann sum?
Quote:

Originally Posted by canyouhelp
Okay, thanks!

I took your word for it. I just did the calculation, and the left-hand Riemann sum with four subintervals would be -11, not -13.5. Did you use 8 subintervals?
• Apr 17th 2014, 02:30 PM
canyouhelp
Re: Help with left hand Riemann sum?
Quote:

Originally Posted by SlipEternal
I took your word for it. I just did the calculation, and the left-hand Riemann sum with four subintervals would be -11, not -13.5. Did you use 8 subintervals?

Oh wow, thanks for catching that! Yes, I messed up and used 8 sections. I need to be more careful about following the question.