Question

Use the law of cosines to find the value of cos. (see pic attached inside!!) Round the answer to two decimal places!

A. 0.84

B. 0.35

C. 0.23

D. 1.23

***not too sure how to solve :/

do i plug into c^2=a^2+b^2 - 2abcos(C) ? :/ @terenzreignz :)

Answer 1

pic!! :)

Answer 2

okay, notation first...
a , b, and c are sides
while
A , B , and C are the angles opposite those respective sides...

savvy? :D

Answer 3

haha savvy :P

Answer 4

There are two incarnations of the law of cosines... they're one and the same, but this one is more convenient for finding the angle...
\[\Large \cos(C) = \frac{a^2+b^2-c^2}{2ab}\]

Answer 5

Plug in and be done :P

Answer 6

okay! :)

so cos(C) = 5.7^2+9.8^2-10.2^2 / 2(5.7)(9.8)

is that right so far?

Answer 7

No... the one with the minus sign in the numerator is the side opposite the missing angle...

Answer 8

a and A are opposite
b and B are opposite
c and C are opposite

you get the idea :D

Answer 9

ahh okay..

so it should be 10.2^2+9.8^2-5.7^2 / 2(10.2)(9.8) ??

Answer 10

Yup :D

Answer 11

:) i got 8376 :/ thats not right is it?

Answer 12

can't be...

Answer 13

yeah.. idk.. i put it into my calc and thats what i got! idk what I'm doing wrong! :(

Answer 14

probably an error
google this
(10.2^2+9.8^2-5.7^2 )/ (2(10.2)(9.8))

Answer 15

calculators are nit picky when it comes to parentheses

Answer 16

okay :)

got this: 0.83828531412

so the answer is A. 0.84 ?

Answer 17

yup :D

Answer 18

awesome! thanks :)