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Find the Equation of a Tangent Line of a Function
The equation for an arbitrary tangent to the graph of a function is given by the point-slope equation:
Formula
Point-Slope Equation
where is the point of tangency and is the slope. After substituting into the formula, you always solve for .
When solving differential equations, you are often asked to find the tangent to a graph at a certain point. It is then useful to use the fact that from the differential equation can be used to find . You do as follows:
Rule
Find the Tangent at a Given Point Using Differential Equations
- 1.
- Solve the differential equation with respect to .
- 2.
- Insert the -value at the point of intersection with the tangent, and find the value of .
- 3.
- Enter , and into the point-slope equation and find the equation for the tangent.
Example 1
Given the differential equation , find the tangent at the point
- 1.
- Solve for :
- 2.
- Insert the point :
- 3.
- Insert this into the point-slope equation: