Differentiating using First Principals
To find the gradient of a tangent at the point A Equation of the tangent takes the form y = mx +c m is the gradient of the tangent
1. Start with a chord of length AB 2. B moves towards A. 3. When B reaches C the chord is getting shorter and closer to A
Gradient AB = x f(x) h x+h f(x+h) A B
Example: Find the gradient of the tangent at any point x
Substituting
Example: Find the gradient of the tangent at any point x Multiply out the brackets
Example: Find the gradient of the tangent at any point x Divide top and bottom by h
Example: Find the gradient of the tangent at any point x h becomes 0
Note: Differentiated gives
Practice: Differentiate from first principals:
Worksheet 1