Question

find the definite integral

Answer 1

\[\int\limits_{0}^{\pi/9} xcos(9x)dx\]

Answer 2

u = x
du = dx

dv = cos(9x)dx

1/9 sin(9x)

Answer 3

\[\frac{x}{9}\sin(9x) - \frac{1}{9}\int\limits \sin(9x)dx\]

Answer 4

\[\frac{x}{9}\sin(9x) - \frac{1}{9} -\cos(9x)+c\]

Answer 5

acutally it should be 1/9cos(9x)

Answer 6

almost,

\[\frac{x}{9}sin(9x)-\frac{1}{9} \int sin(9x) \]

Or did you think about something else? (This is only the first step)

Answer 7

same thing i got, now to do the next step.

Answer 8

you missed multiplying by the 1/9 outside the integral, so it should be:\[\frac{x}{9}\sin(9x) + \frac{1}{81}\cos(9x)+c\]

Answer 9

yup I said I forgot the 1/9 :P

Answer 10

so since this is a definite integral from 0 to pi/9

Answer 11

\[[\frac{\frac{\pi}{9}}{9}\sin(9*\frac{\pi}{9}) +\frac{1}{81}\cos(9 * \frac{\pi}{9})] - [\frac{0}{9}\sin(9*0) +\frac{1}{81}\cos(9 * 0)]\]

Answer 12

\[[\frac{\frac{\pi}{9}}{9}\sin(9*\frac{\pi}{9}) +\frac{1}{81}\cos(9 * \frac{\pi}{9})] - [\frac{1}{81}]\]

Answer 13

cancel the 9's in the sin/cos

Answer 14

and then simplify further

Answer 15

e.g.:\[\sin(9*\frac{\pi}{9})=\sin(\pi)=0\]

Answer 16

do you understand?

Answer 17

yessir.

Answer 18

so what final answer do you get?

Answer 19

what shall I do with pi/9/9

Answer 20

ignore it because it is multiplied by zero

Answer 21

I guess nothing since sin(pi) = 0 so it's just 0...

Answer 22

so it's -1/81 - 1/81 so 1/162?

Answer 23

not quite

Answer 24

oh wait 0?

Answer 25

no...

Answer 26

nvm lol

Answer 27

:)

Answer 28

cos(pi) is -1

Answer 29

sorry my head is about to kerplode.

Answer 30

better wear a crash helmet then :D

Answer 31

:)

Answer 32

so it's not -1/162?

Answer 33

\[-\frac{1}{81}-\frac{1}{81}=-\frac{2}{81}\]

Answer 34

oh.

Answer 35

derp :P

Answer 36

I think you were trying to multiply them

Answer 37

yeah Idk I cannot compute anything anymore LOL

Answer 38

or something?

Answer 39

maybe you need a rest - too much math is not good for your health :)

Answer 40

I know... I need to get this done by midnight soo....

Answer 41

gotta smash through it...

Answer 42

you certainly are persistent - that is a good quality - I'm sure you will go far in life :)

Answer 43

I hope :p

Answer 44

ROUND 2
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