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The derivative as the slope of the tangent line (at a point)

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Presentation on theme: "The derivative as the slope of the tangent line (at a point)"— Presentation transcript:

1 The derivative as the slope of the tangent line (at a point)

2 What is a derivative? A function the rate of change of a function the slope of the line tangent to the curve

3 The tangent line single point of intersection

4 slope of a secant line a x f(x) f(a) f(a) - f(x) a - x

5 slope of a (closer) secant line ax f(x) f(a) f(a) - f(x) a - x x

6 closer and closer… a

7 watch the slope...

8 watch what x does... a x

9 The slope of the secant line gets closer and closer to the slope of the tangent line...

10 As the values of x get closer and closer to a! a x

11 The slope of the secant lines gets closer to the slope of the tangent line......as the values of x get closer to a Translates to….

12 lim ax f(x) - f(a) x - a Equation for the slope Which gives us the the exact slope of the line tangent to the curve at a! as x goes to a

13 similarly... a a+h f(a+h) f(a) f(x+h) - f(x) (x+h) - x = f(x+h) - f(x) h (For this particular curve, h is a negative value) h

14 thus... lim f(a+h) - f(a) h h 0 AND lim f(x) - f(a) x a x - a Give us a way to calculate the slope of the line tangent at a!

15 Which one should I use? (doesn’t really matter)

16 A VERY simple example... want the slope where a=2

17 as x a=2

18 As h 0

19 back to our example... When a=2, the slope is 4

20 in conclusion... The derivative is the the slope of the line tangent to the curve (evaluated at a point) it is a limit (2 ways to define it) once you learn the rules of derivatives, you WILL forget these limit definitions cool site to go to for additional explanations:


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