matlee
  • matlee
Need help with precalculus will give owl bucks
Mathematics
  • Stacey Warren - Expert brainly.com
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SOLVED
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schrodinger
  • schrodinger
I got my questions answered at brainly.com in under 10 minutes. Go to brainly.com now for free help!
matlee
  • matlee
matlee
  • matlee
For each triangle , determine the indicated value
matlee
  • matlee
I know this is Cosine rule, but not sure how to start.

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Zale101
  • Zale101
|dw:1450407256242:dw|
Zale101
  • Zale101
You are right, you need a cosine rule for this. Do you have an idea of what the rule says for cosine?
matlee
  • matlee
To solve a triangle is to find the lengths of each of its sides and all its angles. The sine rule is used when we are given either a) two angles and one side, or b) two sides and a non-included angle. The cosine rule is used when we are given either a) three sides or b) two sides and the included angle.
matlee
  • matlee
matlee
  • matlee
I think its that one
Zale101
  • Zale101
Cosine rule states: \(a^2=b^2+c^2-2bc*cos(A)\) \(b^2=a^2+c^2-2ac*cos(B)\) \(c^2=a^2+b^2-2ab*cos(C)\)
Zale101
  • Zale101
Keep in mind, you are solving for only C. Which is the correct equation to use?
matlee
  • matlee
O lol , c^2
Zale101
  • Zale101
Yes.
matlee
  • matlee
wait thats what i put
matlee
  • matlee
i got confused
Zale101
  • Zale101
You need to use this equation \(c^2=a^2+b^2-2ab*cos(C)\)
matlee
  • matlee
ok
Zale101
  • Zale101
Now, plug the a, c, and b and solve for C. Can you do that?
matlee
  • matlee
wait wait before we proceed can yo usee if i used the right rule for this one
Zale101
  • Zale101
You are right.
matlee
  • matlee
I used thee sine rule
matlee
  • matlee
but cosine rule says if you have two sides and inlcuded angle then use cosine rule but i have included angle and i used sine rule
Zale101
  • Zale101
Yes. Because you got the degree and the side for A and a side for b. All you have to do is: \(\Large\frac{sin(A)}{a}=\frac{sin(B)}{b}\) \(\Large\frac{sin(70°)}{7}=\frac{sin(B)}{4}\) Cross multiply and solve for B, don't forget to use inverse sine to solve for B at the end.
Zale101
  • Zale101
Same thing for cosine rule equation you had, don't forget to use inverse cosine to solve for C.
matlee
  • matlee
o man im so confused i had asked a question earlier and he did it without the inverse cosine
Zale101
  • Zale101
Ok. I have a good idea. How about you show your work here or write it on paper and take a picture of it.
Zale101
  • Zale101
You take the inverse to both sides in order to solve for C.
matlee
  • matlee
Ok thank you i will do it right now. OOO. This one i had to solve for side a
matlee
  • matlee
the one that he did not do inveerse
Zale101
  • Zale101
\(c^2=a^2+b^2-2ab*cos(C)\) Plug these in: a=6, b=12, c=17 \(17^2=6^2+12^2-2(6)(12)*cos(C)\) \(289=180-144*cos(C)\)
Zale101
  • Zale101
Is that what you had?
matlee
  • matlee
haha no i am writing them right now but yes.
Zale101
  • Zale101
I have a question for you.
matlee
  • matlee
Ok
Zale101
  • Zale101
When you knew that you had to use the cosine rule, did you plug in a,b, and c or you did not attempt this question at all?
matlee
  • matlee
No i did not attempt the question at all because i couldnt tell if i did it right, also i just learned this three open study questions ago
Zale101
  • Zale101
Okay, can you show your work here by typing it out?
matlee
  • matlee
matlee
  • matlee
im stuck
Zale101
  • Zale101
\(\Large-\frac{109}{144}=cos(C)\)
Zale101
  • Zale101
What happens if you take the inverse cos to both sides? Have you learned about this before?
matlee
  • matlee
Yes but i barely pay attention in class.
matlee
  • matlee
wait how did u get 109/144
matlee
  • matlee
someone taught me about inverse last open study question
matlee
  • matlee
oh i see because u subrtracted 180 from 289 and since -144 is connected to cos you have to divide
matlee
  • matlee
do i have to use inverse now?
Zale101
  • Zale101
\(289=180-144*cos(C)\) subtract 180 to both sides \(289-180=180-180-144*cos(C)\) \(109=-144*cos(C)\) divide -144 to both sides \(109=-144*cos(C)\) \(\Large \frac{109}{-144}=\frac{-144*cos(C)}{-144}\) \(\Large-\frac{109}{144}=cos(C)\)
Zale101
  • Zale101
Yes, use the inverse now. Here's an example of how an inverse operates. |dw:1450408919922:dw|
Zale101
  • Zale101
\(\Large cos^{-1}(cos(x))=x\) the cosines will reverse and cancel out which will equal x
Zale101
  • Zale101
Do the same when solving for C.
matlee
  • matlee
Ok. Wait what is X?
matlee
  • matlee
nvm i got it lol
matlee
  • matlee
2.42942=x
Zale101
  • Zale101
Yes.. :)
Zale101
  • Zale101
That's your C.
matlee
  • matlee
yay is that C?
Zale101
  • Zale101
X and y are just examples.
matlee
  • matlee
Thank you!
Zale101
  • Zale101
No problem! :)
matlee
  • matlee
Can you vrvbhelp me iwth more!Its not value anymore its are aof triangle
matlee
  • matlee
@Zale101 i want to give you owl bucks but i have 9 and it says i dont have enough to send but i have sent less than 9 before when i had 10 owl bucks.
Zale101
  • Zale101
That's okay. I don't need no owlbucks.
matlee
  • matlee
lol ik now

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