Question

.

Answer 1

so just watch this how to movie first, then we'll go through it together...?

Answer 2

http://www.youtube.com/watch?v=8z6JRFvjkpc

Answer 3

Oh ok!

Answer 4

I think I watched this before; I get how to do the trapezoidal rule when it just gives you like n=a certain number; I just get confused once they give you a table

Answer 5

ok, so your x values are 0 to 8
and you have 5 points
so cut it up into 4 trapeziods

Answer 6

x 0 2 4 6 8
y 17 13 10 9 7

f(x) = y
so integ (0 -> 8) f(x) dx approx = (delta x)/2 [ f{x0} + 2 f{x1} + 2 f{x2} + 2 f{x3} + f{x4} ]
also, in this example:
x0 = 0
x1 = 2
x2 = 4
x3 = 6
x4 = 8
so delta x = (b - a) / n = (x4 - x1)/4
= (8-2)/4
= 6/4
so delta x = 1.5
so integ (0 -> 8) f(x) dx approx = (delta x)/2 [ f{x0} + 2 f{x1} + 2 f{x2} + 2 f{x3} + f{x4} ]

Answer 7

(1.5)/2 [ 17 + 2 {13} + 2 {10} + 2 {9} + 7 ]
0.75 times [ 17 + 26 + 20 + 18 + 7 ]

Answer 8

why isn't it (x4-x0)? or is that just how the formula is

Answer 9

=0.75 {88}
=66

Answer 10

i think its just how the formula is, we dont include x0, its x1 in the formula as x0 is just a starting point, there will always be 1 fewer trapeziods than there are points
so if we have x0 to x20, it will be x20 - x1/19, as there will only be 19 trapezoids...
i think

Answer 11

And why did you write 1.5/2?

Answer 12

Oh wait nevermind

Answer 13

I got it :)

Answer 14

sorry

Answer 15

Are you sure about the x4-x1 thing though?

Answer 16

Because I think the answer is supposed to end up being an estimation

Answer 17

no, not sure, we did this last yr, so a bit fuzzy.... maybe it is b = 8 and a = 0
... yeah, think you're right there, sorry

Answer 18

So 8-0=8/4=2/2=1?

Answer 19

Sorry I'm just confused :s

Answer 20

sók, sorry im kinda fumbling from memory here too :(
so yeah, delta x = 2
so delta x / 2 = 1
so area under curve approx = 88 then?

Answer 21

I think? It just says that the answer will be an estimate and I don't know why

Answer 22

Like an estimate decimal thing

Answer 23

because the trapeziods arent following the exact curve of the line, only the approximate curve
that's why it's an estimate

Answer 24

Well okay, I'm gonna take your word for it :)

Answer 25

sçool, that last one im pretty much 100% sure on, and about 80% sure our maths is right too now ;)

Answer 26

And it is (x4-x0) for suuure? :p

Answer 27

just looked it up.... looks like ur right
http://www.mathwords.com/t/trapezoid_rule.htm
a = x0
b = x4

Answer 28

jus make sure you never double the first and last point in this eqn
so integ (0 -> 8) f(x) dx approx
= (delta x)/2 [ f{x0} + 2 f{x1} + 2 f{x2} + 2 f{x3} + f{x4} ]
see how f(x0) and f(x4) aren't doubled, but all the other points are...?

Answer 29

Yes, I see

Answer 30

sweeet, gud luck and i hope we're right ;)

Answer 31

Okay thanks :) me too