Question

How do I solve ABC?

I dont want the answer, I just need to know how to solve it.

Answer 1

you know cosine rule right??

Answer 2

law of cosines, I believe... if you are talking about solving for the length of BC, which would in turn enable you to use the law of sines to solve for all of the triangle.

law of cosines is as follows:

a^2 = b^2 + c^2 - 2bc * cosA

where a,b,c are lengths along the triangle, and cosA is an angle measurement.

cosA = 58 degrees
b = 12.3
c = 14.6

a = ?!?!?!? solve for a, and you can then find the other angles if you want

Answer 3

a² = b²+c² - 2bc cos(a) right?

Answer 4

yup, using this rule, you should be able to solve everything on this triangle, first c, than angles, and other angle.

Answer 5

ok, so i get 174.12

Answer 6

and that is for a²

Answer 7

Therefore, a = 13.2?

Answer 8

use the generalized pythag thrm for finding the missing side; then use law of sines to facilitate the rest

Answer 9

For finding angel B, I use the sine law right?

Answer 10

the angles are easier found using the law of sines, yes

Answer 11

both would work ... sine is faster and simpler than cosine.

Answer 12

yeah a = 13.2

and law of cosines is terrible for finding angles unless you want to do all that work again.

law of sines is ez

Answer 13

terrible? lol; its actually perfect for finding angles, just alot more work is all :)

Answer 14

Alright, Thanks so much all of you:) I really appreciate it

Answer 15

less work = better, efficiency is key!

although terrible is probably a harsh word lol, i'm sorry cosine law i did not mean to hurt your feelings

Answer 16

\[cos^{-1}\frac{c^2-a^2-b^2}{-2ab}=C\]

Answer 17

there are certain condition where the law of sines will throw out a bad value; something to do with a triangle that can have 2 different results.