To find the radius of this Brazilian coin, first multiply 3.14 by 2. This will give you and answer of 6.28. Then, divide 84.78 mm by this, and you will get your radius of 13.5.
The formula for circumference is C = πd or C = 2πr. In this case, we want the radius, so we can use the formula that has the radius in it. Since C = 84.78, substitute to get 84.78 = 2πr. Divide both sides of the equation by 2π, which is equal to 6.28. The radius is 13.5 mm.
Answer: We will see in the next example how using the Quadratic Formula to solve an equation with a perfect square also gives just one solution. Solve 4{x}^{2}-20x=-25
