A plane took off at a 15° angle to the ground and flew in Sydney’s direction. She is standing at a point 25 miles from the point where the plane took off. If the plane has traveled 20 miles in the air, about how far is Sydney from the airplane? Round your answer to the nearest whole number.

The plane’s 20-mile flight path and the 25-mile ground distance form a triangle with an included angle of 15°. Use the law of cosines: the distance from the plane to Sydney is √(20² + 25² − 2·20·25·cos 15°) ≈ 7.7 miles. Rounded to the nearest whole number, that is 8 miles, choice A.

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