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Math.PI

Besides functions Math offers some mathematical constants. Math.PI gives π (roughly 3.14) and Math.E gives Euler's number e (roughly 2.71).

Exercise

Write a function area that calculates the area of a circle. The function is given the radius of the circle.

Example: area(1) should return π and area(2) should return 4 * π.
function area(r) {
  return Math.PI ... ;
}
function area(r) {
  return Math.PI * r * r;
}

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