math_struggler
New member
- Joined
- May 27, 2014
- Messages
- 6
I'm having trouble with where to start. I tried to find the value of x by using the cos rule with 6/x but I'm unsure of how I would apply the cosine to derive the following equation.

The diagram shows the triangle ABC in which angle A = pi/6
AB = 6cm and BC = 4cm
Let AC = xcm
a) Use the cosine rule to derive x2 - 6sqrt(3)x + 20 = 0
b) Use the quadratic formula to show AC has length 3sqrt(3) - sqrt(7) or 3sqrt(3) + sqrt(7)
Though, I'm sure if I had help figuring out (a) I would more than likely be able to solve (b).
Here's to hoping!
Thanks

The diagram shows the triangle ABC in which angle A = pi/6
AB = 6cm and BC = 4cm
Let AC = xcm
a) Use the cosine rule to derive x2 - 6sqrt(3)x + 20 = 0
b) Use the quadratic formula to show AC has length 3sqrt(3) - sqrt(7) or 3sqrt(3) + sqrt(7)
Though, I'm sure if I had help figuring out (a) I would more than likely be able to solve (b).
Here's to hoping!
Thanks