# Tangent to a circleWatch

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#1
From differentiation I have learned that the equation of a tangent is
derived from setting the differentiated result to the value of x at
that particular point (the gradient) and then..

is y-y = grad(x - x)

and the normal being perpendicular grad becomes grad * inverse = -1

i.e. 3/4 becomes - 4/3

Now i'm doing circles, and find that in one of the book's examples working out
the equation of the tangent to a circle, they are using the inverse of the
gradient as if it were for a normal.

Am I missing something?

Jorge
0
14 years ago
#2
(Original post by Jorge)
From differentiation I have learned that the equation of a tangent is
derived from setting the differentiated result to the value of x at
that particular point (the gradient) and then..

is y-y = grad(x - x)

and the normal being perpendicular grad becomes grad * inverse = -1

i.e. 3/4 becomes - 4/3

Now i'm doing circles, and find that in one of the book's examples working out
the equation of the tangent to a circle, they are using the inverse of the
gradient as if it were for a normal.

Am I missing something?

Jorge
tangent meets radius at right angles.
so if tangent meets circle at (x,y)
the line through centre of circle and (x,y) and the tangent line will be perpendicular.
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