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Math help!!

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comeatmebro
Posts: 10720 - Karma: 66
alright so i need some help with these problems, and if you can let me know how you did them. that would be awesome.

1. Find sin(theta) when cos(theta) is -.53170 and theta is in quadrant 3.

2. Combine the parametric equations y=5cos(t) and x=3sin(t) into one equation relating y to x.

3. Solve for side a, b and angle B






/ \
/ \
22.7 / \a
/_________\
^ b
Jun 2 2008 8:40PM
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comeatmebro
Posts: 10720 - Karma: 66
FUCK! my triangle got fucked up. and it didn't post my shit...


okay basically it is a regular looking triangle. i have the bottom left angle measure of 48 degrees and bottom right angle measure of 37 degrees. also i know the left side is 22.7 units. i need to find the two missing side lengths. using law of cosines/sines.



any help would be awesome, +++ karma given out. it's for my final so it would be nice to get these right haha.
Jun 2 2008 8:42PM
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1080ski
Posts: 4424 - Karma: 191
ahh, i finished highschool a few weeks ago, but ill help you out.

for 2:

y=5cos(t)
x=3cos(t)

so you can solve for cos(t):

1/5y=cos(t)

substitute cos(t) in the x equation and get:

x=3(1/5y) = x=3/5y

so solve for y from that equation
Jun 2 2008 8:45PM
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1080ski
Posts: 4424 - Karma: 191
for 3:

you can find out that the last angle = 95 (all angles add to 180)

use law of sines, which is sin(a)/a = sin(b)/b = sin(c)/c

so we have the first angle (bottom right), lets call it a, and the first side (the 22.7 long one), call that side a.

sin(37)/22.7 = sin (48)/b = sin (95)/c

solve for that, and you should get your answer


that should work, but my math is a little rusty
Jun 2 2008 8:52PM
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comeatmebro
Posts: 10720 - Karma: 66
sweet. thanks. karma +++'ed haha. the #2 one i had no clue on, but i think i got it. and this one i can't find my notes on law of sines so i just needed the equation so that's done too. now i just need this peksy #1. i have no clue how to do it.

our completion part of our math final is two days, i figured why finish when i can do the problems at home, then get a hundred tomorrow. so here i am haha.
Jun 2 2008 8:55PM
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Jacuse
Posts: 1792 - Karma: 1,549
damn, I have a final on this in three days and I completely forgot how to do this shit.
Jun 2 2008 8:55PM
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comeatmebro
Posts: 10720 - Karma: 66
yeah dude i am generally good in math, but it's too much to remember. like i can't remember ALL of these equations and stuff...shit sucks. tomorrow is my last day for finals then on to junior year haha.
Jun 2 2008 8:57PM
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1080ski
Posts: 4424 - Karma: 191
my bad, forgot the last part for 3. i found a and b to be 22.7 (given) and 27.01 (the side opposite the angle equal to 48). i used
c2 = a2 + b2 – 2ab cos C, the law of cos, to find the last side, which i got to be 18.694. im sorry if i fucked this up but i tried haha... im working on 1. and i donno why my font went like this
Jun 2 2008 8:57PM
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steezyjibber
Posts: 15967 - Karma: 11,016
you get some equations and stuff for the final
Jun 2 2008 9:02PM
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comeatmebro
Posts: 10720 - Karma: 66
what?
Jun 2 2008 9:03PM
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Jacuse
Posts: 1792 - Karma: 1,549
yeah same, I get it when we learn it and all, but after a few weeks I forget most of the formulas. A few times I have stored the formulas in my calculator that I just can't remember.
Jun 2 2008 9:06PM
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1080ski
Posts: 4424 - Karma: 191
oops, didnt see you got 3.

here is 1:

think of a circle with a center (0,0) with a radius of 1 (so any point on the circle is 1 unit away from the center)

the angle is in quadrant 3, so draw a line going out into q 3 from the center, and connect that line to the x axis, making a triangle.

mark the radius as 1, because we made it equal to 1. the height is y, the length is x (but remember, x and y are negative numbers because they are in quadrant 3).

you have cos (theta) = -.53170. cosine equals A/H (adjacent over hypotenuse), so you have x/1 = -.53170, because the H= 1 and A = x.

solve for x, and you get x=-.57310. now you have 2 sides of a right triangle. use the pythagorean theorem to solve for y (remember though, it is negative). you should get y = -.8469 (may have messed up the decimals but its close to that).

since sin = O/H, opposite/hypotenuse, just fill in the numbers you have. you will get -.8469/1, which equals -.8469


if i messed up somebody let him know so he doesnt take my info and fail haha.
Jun 2 2008 9:06PM
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ChanchoVelez.
Posts: 1029 - Karma: 11
fuck it i hate math
Jun 2 2008 9:07PM
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comeatmebro
Posts: 10720 - Karma: 66
sick. that seems right, and rings a bell. now i just have to remember these for tomorrow and i'm good to go.
Jun 2 2008 9:10PM
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killa_cam
Posts: 13143 - Karma: 15
good stuff, but for one, it's much easier if you remember that cos^2ø + sin^2ø = 1 rather then what homie said up there
Jun 3 2008 12:29AM
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killa_cam
Posts: 13143 - Karma: 15
this can be proved a number of ways, so if you actually need a proof let me know and i'll type one up
Jun 3 2008 12:32AM
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spliff.Life
Posts: 7847 - Karma: 1,549
start a math help cult
Jun 3 2008 12:41AM
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purplejumpsuit
Posts: 2207 - Karma: 157
shitt I have a test on all this stuff tomorrow and I forget most of it also.
Jun 3 2008 1:14AM
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