Thread: Am I doing something wrong?

Algebra II: Equations and Triangles - Math for Morons Like Us

Scroll down the page until you hit the part that says Law of Cosines.
I have been trying to solve that problem for hours now and I don't get the same answer for Angle A.

Here is the problem.

--------------------------------------------------------------
1. Problem: In triangle ABC, a = 24,
c = 32, and angle B = 115o.
Solve the triangle.

Solution: We know two sides. Find the third
using the law of cosines.

b2 = a2 + c2 - 2ac(cos B)

Plug in any known information.

b2 = 242 + 322 - 2 * 24 * 32(-.4226)
b2 = 2249

Solve for b by taking the square
root of each side.

b = SQRT(2249) = 47.4

Using the law of sines,
angle A = 27.32o.

Since we know that triangles are made of
three angles that sum to 180o,
we can find the measure of angle C by
setting up an equation.

Angle C = 180o - 115o - 27.32o = 37.68
----------------------------------------------------------------

After reaching the part where is says.
Using the law of sines,
angle A = 27.32o.
I am unable to get angle A = 27.32 I keep getting A = 29.55

Here is the formula I keep using.

(24(Sin115))/(Sin(47.4)) = 29.55

I don't get how the answer is 27.32

Can anyone please tell me if I am doing something wrong or if the site is wrong...

(Special request: Does anyone know of a good site like the one I posted with step by step instructions on Trigonometry and such.)

Originally Posted by Brazuca

Here is the formula I keep using.

(24(Sin115))/(Sin(47.4)) = 29.55

I don't get how the answer is 27.32

Can anyone please tell me if I am doing something wrong or if the site is wrong...

I thought 47.4 is distance? There is no sine value for a distance.

I understand now, what I had to do.

(24(Sin115))/(47.4)) = .45889

Then Sin^-1(.45889) = 27.3

Thanks.