EXAMPLE 1 (a) If x^2 + y^2 = 100, find dy/dx.
(b) Find an equation of the tangent to the circle x^2 + y^2 = 100 at the point (8, 6).
SOLUTION 1 (a) Differentiating both sides of the equation x^2 + y^2 = 100:
Remembering that y is a function of x and using the Chain Rule, we have
Thus
Now we solve this equation for dy/dx:
(b) At the point (8, 6) we have x = 8 and y = 6, so
An equation of the tangent to the circle at (8, 6) is therefore
or