# NEED Help (Basically a Law of Cosines problem)

In summary, the conversation discusses a problem involving finding the lengths of cables AC and AB after elongation. One person suggests using similar triangles, but it is determined that the angles will change and the method will not work. The other person suggests using the Law of Cosines to solve the problem. They also exchange some friendly banter about their classes.
[SOLVED] NEED Help (Basically a Law of Cosines problem)

So in this problem, all I have to do is to solve it is find out by how much cables AC and AB elongate.

I thought I could just break it into two Right triangles and just use similar triangles (before and after elongation)

If you look at the upper right triangle, let's call it ACO, where O denotes the point on the wall halfway between C and B.

Then I tried doing,
$$\frac{AC}{OA}=\frac{AC'}{OA'}$$

$$\Rightarrow AC'=\frac{300}{300\cos30}*(300\cos30+2)$$

But this does not work. . . why the hell not??

My prof gave us the hint: "Use Law of Cosines to find the lengths of AC or AB after elongation"

How do I use Law of Cos if I don't know the angles after elongation, and moreover what is wrong with the process I tried?

I hate all of my classes. I miss physics.

Casey

Mechanics of Materials eh?

http://www.mediafire.com/?0fmwmgeogi6

Last edited by a moderator:
Where did you get that? Anyway, thanks! I think the dotted line should be labeled $L_{AC}'$ though. But now I see it. I never took a geometry course so this stuff makes me insane.

Do you know why my original method does not work?

because they won't be similar triangles...

coffeebean51 said:
because they won't be similar triangles...

ummm. . . because the angle changes right?

Yeah.

Short and to the point. I like your style beans

Welcome aboard,
Casey

## 1. What is the Law of Cosines?

The Law of Cosines is a mathematical formula that relates the lengths of the sides of a triangle to the cosine of one of its angles. It is used to solve for missing sides or angles in non-right triangles.

## 2. How do you use the Law of Cosines to solve a problem?

To use the Law of Cosines, you need to have at least three pieces of information about the triangle - either three sides or two sides and the included angle. Then, you can plug these values into the formula and solve for the missing side or angle.

## 3. Can the Law of Cosines be used for any triangle?

Yes, the Law of Cosines can be used for any triangle, whether it is a right triangle or not. However, it is most commonly used for non-right triangles.

## 4. What is the difference between the Law of Cosines and the Pythagorean Theorem?

The Pythagorean Theorem only applies to right triangles, while the Law of Cosines can be used for any triangle. Additionally, the Pythagorean Theorem only relates the squares of the sides, while the Law of Cosines relates the actual lengths of the sides.

## 5. Are there any restrictions or limitations when using the Law of Cosines?

Yes, the Law of Cosines can only be used to solve triangles. It cannot be used for other shapes or figures. Additionally, the given information must be accurate and complete for the formula to work correctly.

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