Question

In triangle ABC, a = 9, c = 5, and angle B = 120°. Find the measure of angle A to the nearest degree. Show your work.

Answer 1

hurr-durr

Answer 2

huh? lol @PeterPan

Answer 3

Just what I said. hurr-durr.

Now this appears to be nothing more than a law-of-cosines problem :)

Answer 4

Yes, I did it but i got stuck and i did it again then i got stuck again. I used c^=a^2+b^2-2(a*b)cos(x)

Answer 5

@PeterPan

Answer 6

You should find b first.
\[\large b^2 = a^2 + c^2 -2ac \ \cos(B)\]

Answer 7

okay one sec @PeterPan

Answer 8

i did b^ = 9^ + 5^ - 2(9*5)cos(120) and i got 151...now what? @PeterPan

Answer 9

well that's b^2 isn't it?
get its square root ^^

Answer 10

yes and now i got 12.2 @PeterPan

Answer 11

I don't know.... maybe include three decimal places to be safe?

Answer 12

okay now what? @PeterPan

Answer 13

Well, you have angle B and side b, and you have side a.

Use the Law of Sines now ^^

Answer 14

\[\Large \frac{\sin(A)}{a}=\frac{\sin(B)}{b}\]

Answer 15

2.01=.023?? oh gosh i suck @PeterPan

Answer 16

Best way to fix is to show your work. Then we'll see what went wrong ^^

Answer 17

sin9/9 = sin12.288/12.288 i crossed multiplied @PeterPan

Answer 18

a is not the same as A silly :P
A is your missing angle
a is the side length (9)
b is also a side length (the one you just found, 12.288)
B is the angle (120 degrees)

Let's try again, shall we?

Answer 19

okay sin(120)*9=7.79 but what to do for A since i dont know it? im sorry @PeterPan

Answer 20

that's what we're trying to find, silly :P

Answer 21

Ohh okay . so.. 12.288sin(A)=2.133 soooooooooooooo 7.79=2.133 @PeterPan

Answer 22

it's really confusing with you skipping steps, so could you please show your work, step-by-step? :)

Answer 23

i need to know where you're getting all this.

Answer 24

okay lol 12.288sin(A)= 2.133 AND SIN(120)*9=7.79 @PeterPan

Answer 25

where does 2.133 come from?

Answer 26

NOOOOOOOOOOOO I GOT IT I GOT IT ! OKAY SO 12.288SINA=7.79 THE I DIVIDED 12.288 ON BOTH SIDES WHICH GAVE ME SINA=.634 THEN I DID SIN-1(.634 WHICH GAVE ME 39.3 @PeterPan

Answer 27

That's more like it ^^

Answer 28

Lol thanks for helping me. Even though i was so hard to help I bet !

@PeterPan

Answer 29

no worries ^^