# Help With The Law of Sines

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1. May 23, 2016

### MathWA

1. The problem statement, all variables and given/known data

Find a by using The Law of Sines by knowing that c=12, angle A=42o, angle C=69o.
2. Relevant equations
(sin A)/a=(sin B)/b=(sin C)/c

3. The attempt at a solution
I tried putting it in, but all I got was this correct, but useless equation:
6511/7990=383/470
I did it 1 more time, but still it wasn't successful.

2. May 23, 2016

### rpthomps

I am not sure how you go the numbers you did in the solution attempt. The sine of the angles will give you numbers less than 1. I get the answer 8.6 for a

3. May 23, 2016

### MathWA

Well, I did a lot of factoring with decimals, so I must had got them mixed up.
By the way calculators are allowed.

4. May 23, 2016

### MathWA

The answer is actually 9.34, but I need the solution(step-by-step work).

5. May 23, 2016

### rpthomps

6. May 23, 2016

### MathWA

I recalculated and got 61, instead, but its wrong!

7. May 23, 2016

### MathWA

Well, I got c equals to 50.

8. May 23, 2016

### rpthomps

Can you write out line by line what you are doing, please?

9. May 23, 2016

### MathWA

That would take a while, but sure, but not now(I'm very busy)
I can give you the last couple of lines:
(0.94)/a=47/ac
c=50
0.94/a=0.77/50
47=0.77a

10. May 23, 2016

### rpthomps

well, firstly if 0.94 is your answer to sin42, that isn't right. I get something closer in radian mode.

11. May 23, 2016

### MathWA

Oops, I typed the wrong problem!
c is 12, angle A is 110, and angle C is 50

12. May 23, 2016

### rpthomps

So, is this work using the new values then? where did 47 come from?

13. May 23, 2016

### rpthomps

$$\frac{a}{sin110}=\frac{12}{sin50}$$

This is how I would start it. THen I would use algebra to solve for the unknown.

14. May 23, 2016

### MathWA

I figured the problem out! Thank you, rpthomps!

15. May 23, 2016

### MathWA

I made the problem too confusing!

16. May 23, 2016

### Staff: Mentor

Yes, this is useless. Since you're trying to solve for a, your equation here should have a in it somewhere.
That's not how it works here. We'll help you get to a solution, but we aren't going to give it to you step by step.