Trigonometry
posted by Britt on .
I am trying to help my child out with a problem but yeah I am finding it veyr hard.
Gabe is spending two weeks on an archaeological dig. He finds a fragment of a circular plate that his leader thinks may be valuable. The arc length of the fragment is about 1/6 the circumference of the original complete plate and measures 1.65 inches. A similar plate found earlier has a diameter of 3.14 inches.
Write an an expression for the radius, r, of the earlier plate.
r=2π
r=π/4
r=π/3
r=π/2
What is the measure, in radians, of a central angle, θ, that intercepts an arc that is 1/6 the length of the circumference of a circle?
θ=2π/6
θ=2π/5
θ=2π/4
θ=2π/3
Write an expression for the arc length, S, intercepted by this central angle
Could Gabe's plate be a matching plate? Explain.

Write an an expression for the radius, r, of the earlier plate.
The earlier plate has a diameter of 3.14 inches, approximately equal to π inches.
The radius equals half the diameter.
What is the measure, in radians, of a central angle, θ, that intercepts an arc that is 1/6 the length of the circumference of a circle?
The central angle of a complete circle is 360°, or 2π radians.
So the central angle of an arc equal to 1/6 of the circumference is therefore 1/6th of the complete circle. Therefore the central angle is (1/6)*2π.
Write an expression for the arc length, S, intercepted by this central angle
The arc length of radius r and central angle θ is rθ. Since r and θ are known, solve for arc length.
Could Gabe's plate be a matching plate? Explain.
It is most likely a matching plate, because the 1/6th of the arc of the previous plate has an arc length of 3.14*π/6=1.643, well within the accuracy expected of the later plate.