Math CentralQuandaries & Queries


Question from azman, a student:

Find the equation of the tangent line to the circle x^2+y^2=9 at the point P (2, square root of 5).

Hi Azman,

There are two facts you can use to solve this problem.

  1. The circle $x^2 + y^2 = 9$ has center $(0,0)$ and radius 3.

  2. The tangent to the circle at P is perpendicular to the radius from the center of the circle to P.

Write back if you need more assistance,

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