What is the equation for the tangent line of a circle with the point on the circle (-1, 2). center of circle (2, -1). i just cant remember the formula. thanks.(worried)

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- May 23rd 2009, 12:11 PMgabbyCalculus
What is the equation for the tangent line of a circle with the point on the circle (-1, 2). center of circle (2, -1). i just cant remember the formula. thanks.(worried)

- May 23rd 2009, 01:03 PMskeeter
slope of the radius connecting the center of the circle to the point on the circle ...

$\displaystyle m_r = \frac{2-(-1)}{-1-2} = -1$

slope of the tangent line is the opposite reciprocal of $\displaystyle m_r = -1$ ...

$\displaystyle m_T = 1$

tangent line equation ...

$\displaystyle y - 2 = 1[x - (-1)]$