$\"\"$

The area of the circle is $\"\"$ .

The area of the ellipse is $\"\"$ .

The are of the ellipse is double the area of the circle.

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$\"\"$ .

The legth of the major axis is $\"\"$ .

Substitute $\"\"$ .

$\"\"$ .

Therfore, the length of the major axis is $\"\"$ .

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The length of the major axis is $\"\"$ .