



 
Hi Andrew, The key to this problem is that if $C$ is the centre of a circle and $P$ is a point on the circle then the tangent to the circle at $P$ and the radius $CP$ are perpendicular. What is the centre $C$ of the circle $x^2+y^2=25?$ What is the slope of the line segment from $C$ to $P(4,3)?$ What is the slope of the tangent to the circle at $P?$ What is the equation of this tangent? Penny  


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