## anonymous one year ago Write the summation to estimate the area under the curve y = 2x2 + 1 from x = 0 to x = 4 using 4 rectangles and left endpoints.

1. anonymous

https://gyazo.com/10fefff1c824a71908fefa15fce74b76 It's A, right? Just making sure I got the right answer, haven't don math in quite some time.

2. anonymous

@dinamix

3. dinamix

yup its great mate @Ephemera

4. anonymous

I got it wrong :(

5. zzr0ck3r

@dinamix this is once again why just giving answers can be bad, you don't know the answer is wrong that you gave...

6. zzr0ck3r

@Ephemera would you like to learn how to do this?

7. dinamix

lol @zzr0ck3r he tell me do that

8. anonymous

Of course @zzr0ck3r

9. zzr0ck3r

remember we don't start at the beginning of the interval, which here you chose 0. If we put it into 4 parts, from 0 to 4, we would use the interval [0,1], [1,2], [2,3], and [3,4]. When we take the width of the first interval, we have 1, so we start at 1 not 0. So what is the right answer?

10. anonymous

It would be D, right?

11. zzr0ck3r

correct

12. zzr0ck3r

remember last time, $$x_1=4.5$$ not $$4$$ even though we were on the interval $$[4,6]$$.

13. dinamix

$\sum_{i=1}^{4}(2i^2+1) = 3+9+19+33$ @Ephemera i think should be like that

14. anonymous

So if it was for example 3 to 5, I'd divide it into 3,3.5,4,4.5?

15. zzr0ck3r

once again, @dinamix just giving the answer would not help really, with logic and reasoning you can lead them to the correct answer.

16. zzr0ck3r

@Ephemera yes, if they said 4 intervals

17. zzr0ck3r

well no, it would be 3.5, 4, 4.5, 5

18. zzr0ck3r

this is assuming they want right triangles, which is pretty normal

19. zzr0ck3r

but the intervals would be [3,3.5], [3.5,4], [4,4.5], [4.5, 5]

20. anonymous

Ok, think I got it I reset my exam because I got a low grade on the last....can you check over my work @zzr0ck3r?

21. dinamix

@zzr0ck3r wow u are good teacher i like u ;)

22. zzr0ck3r

Just post questions as you have them, I am not sure how ethical that is...