3.6. Applications
Tangent Line \& Normal Line Equations
Example 1:
Find the equation of tangent and normal to the circle \( x^{2}+y^{2}=5 \), at the point \( (2,3) \).
Solution 1: \( y=m x+b \) where \( m= \) slope, \( b=y \)-intercept
\[
\begin{array}{l}
y=\left(5-x^{2}\right)^{\frac{1}{2}} \\
y^{\prime}=\frac{1}{2}\left(5-x^{2}\right)^{-\frac{1}{2}}(-2 x) \\
y^{\prime}(x=2)=\frac{1}{2}\left(5-(2)^{2}\right)^{-\frac{1}{2}}(-2(2))=-2 \\
y=-2 x+b \Rightarrow 3=-2(2)+b \Rightarrow \therefore b=7 \\
\therefore y=-2 x+7
\end{array}
\]
2005