# Cosine rule help!

1. Nov 13, 2011

### Con Air

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

Hello! I've run into a problem at work and need a quick solution! Basically I need to work out the cut size of a curved bar. I have the chord length (650mm) and the radius' (1335mm) Obviously i need to calculate the inner most angle, then multiply my diameter by pi, divide by 360 then multiply by my new found angle to find arc length

2. Relevant equations

Cosine rule A=b$^{2}$+c$^{2}$-a$^{2}$$/$2bc

C=∏d

3. The attempt at a solution

obviously c and b are both equal at 1335mm. so the triangle becomes isosceles

Arc length = ∏x2670/360 x (1335$^{2}$+1335$^{2}$- 650$^{2}$/2x1335x1335)$^{cos-1}$

this equation leaves us at 28.17°

then (2670x∏/360)x28.17=656mm

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

2. Relevant equations

3. The attempt at a solution

2. Nov 13, 2011

### LawrenceC

I get 656.6 mm. You did it correctly.

3. Nov 13, 2011

### Con Air

thanks very much, I've never applied that sort of trigonometry to my work before, i was abit unsure! thanks very much for your help.