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.

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1. Problem: InWe know two sides. Find the thirdtriangle ABC,a = 24,

c = 32, andangle B = 115o.

Solve the triangle.

Solution:

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 forbby 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 to180o,

we can find the measure ofangle Cby

setting up an equation.

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

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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.)