Question

Let's start off easy :) trig help???

Answer 1

pi/18

Answer 2

i messed up my equation let me reqrite

Answer 3

\[\Huge \cos3x= -\frac{ 1 }{ 2 }\]

Answer 4

sorry

Answer 5

2pi/9

Answer 6

\Huge Also Solve , [0,2pi)

Answer 7

can you please explain why its that?

Answer 8

unit circle memorization. it shows us that cos-1(-1/2) is 2pi/3 and were looking for 1/3 of that since its 3x so therefore its 2pi/9
heres a unit circle

http://www.google.com/imgres?imgurl=http://upload.wikimedia.org/wikipedia/commons/thumb/4/4c/Unit_circle_angles_color.svg/720px-Unit_circle_angles_color.svg.png&imgrefurl=http://en.wikipedia.org/wiki/Unit_circle&h=225&w=225&tbnid=NHFRVspjd-vZrM:&zoom=1&tbnh=186&tbnw=186&usg=__sOrTVeIoKl48_TodEan8dIx7UGk=&docid=D09vYD7H2hKF-M&itg=1&sa=X&ei=yjZLU-WNBMie2wXK2IDQDg&ved=0CIYBEPwdMAo

Answer 9

2pi/9 = -(1/2)???

Answer 10

(3)*2pi/9 =-1/2 you were looking for x and you had cos(3x) so yeah

Answer 11

o wow i understand -.-

Answer 12

u meant i shoud move cos to the other side.

Answer 13

boom... cos-(1/2) = 3x

Answer 14

\[\huge\frac{ 2\pi }{ 3 } * \frac{ 1 }{ 3 } = x\]

Answer 15

is that what you meant?

Answer 16

no because you have to take the inverse of cosine because cosine of 1/2 is not the same as cos(3x) memorize the unit circle because it makes calc a lot easier. you need to look for where cosine would be -1/2 which is at 2pi/3 and to solve for x from there you just need to divide 2pi/3 by 3

Answer 17

I'm sorry if this isn't making perfect sense but its been 4 years since I took precalc and I'm not sure how to word it other than "well that's the way it is"

Answer 18

i got x = 2pi/9 though lol

Answer 19

hmm

Answer 20

let me c

Answer 21

that is right though

Answer 22

peachy we did the same thing....................................................

Answer 23

-____________________-

Answer 24

we just worded it differently

Answer 25

but cosine of -1/2 is .87758 so when you wrote what you did I didn't follow your steps

Answer 26

"boom... cos-(1/2) = 3x" cuz this doesn't make sense

Answer 27

I don't understand now why did you go into decimals? o-o

Answer 28

ahhhh i shifted the cos from cos3x to the other side.^^^

Answer 29

yeah math won't let you do that directly

Answer 30

so it became 3x = cos -(1/2) from cos3x -(1/2)

Answer 31

oh

Answer 32

thats where we differ because the only way to do that is to take the inverse of cosine do you know what that is?

Answer 33

no please explain :D

Answer 34

cos(0)=1 so the inverse of cosine (or cos^-1(x)
cos^-1(1) = 0

Answer 35

its just a way of flipping them

Answer 36

oh i get it

Answer 37

now how did u apply it to this equation again?

Answer 38

so to solve this youre going to wanna take the inverse cosine of -1/2

Answer 39

mhm

Answer 40

and when you look at the unit circle which i linked above you can see that cosine = -1/2 when cos(2pi/3) do you follow me so far

Answer 41

yes

Answer 42

inverse cosine of -1/2 is 120 = 2pi/3

Answer 43

you need to solve so 3x = 2pi/3 now

Answer 44

oh ok i seee ittt

Answer 45

to fit the equation you were given and then 2pi/9

Answer 46

divide by 3 3on both sides then we're golden

Answer 47

so you followed all of that?

Answer 48

yep thank you

Answer 49

feel free to message me for more help! sorry I took so long explaining =/

Answer 50

its fine you helped a lot.

Answer 51

\[\Huge \sin2x+sinx = 0\]

Answer 52

how would i go about solving this within [0,2pi)

Answer 53

sin2x = 2sinxcosx

Answer 54

yep so set that equal to -sin(x)

Answer 55

2sincosx = -sinx???

Answer 56

yes maam

Answer 57

divide a sin over

Answer 58

awesome thanks

Answer 59

then easy peasy from there right?

Answer 60

when i do identities and solving I always feel like i dont know it and am stuck but then someone tells me and im like OHHHHHHHHHHH i just dont remember the identity unless someone helps me recall it

Answer 61

snxcosx=1

Answer 62

make flashcards for identities it helps

Answer 63

wait am i right?

Answer 64

do i like square both sides or something

Answer 65

wait for the problem we were working on

Answer 66

yep we're now at sinxcosx = 1

Answer 67

no we had 2*sin(x)*cos(x)=-sin(x)

Answer 68

right?

Answer 69

yes

Answer 70

i wrote something wrong mb

Answer 71

i forgive you ;)

Answer 72

divide a sin over and we get 2cos(x)=-1

Answer 73

then cos(x)=-1/2

Answer 74

cosx = -1/2

Answer 75

girl why do you still have a sin there