A circle with circumference 20 has an arc with a 72º central angle.
What is the length of the arc?

l = x · c / 360

l = 72 · 20 / 360

l = 1440 / 360

l = 4

Step-by-step explanation:

1. write down the arc length formula.

2. replace x and c by their values

3. multiply and then divide to get l

it's equivalent, so we can say that its equal.

let's call the denominator x and the numerador is 18 less then denominator, x - 18.

multiply

2.x = 5.(x - 18)

2x = 5x - 90

90 = 5x - 2x

90 = 3x

x = 90/3

x = 30

so: