Chapter 17.2 The Derivative. How do we use the derivative?? When graphing the derivative, you are...
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Transcript of Chapter 17.2 The Derivative. How do we use the derivative?? When graphing the derivative, you are...
Chapter 17.2 The Derivative
How do we use the derivative??
When graphing the derivative, you are graphing the slope of the original function.
Graphing
Which is the f(x) and which is f’(x)?The derivative is 0 (crosses the x-axis)
wherever there is a horizontal tangentY1 = f(x)Y2 = f’(x)
Notation
There are lots of ways to denote the derivative of a function y = f(x).
f’(x) the derivative of f the derivative of f with y’ y prime respect to x.
the derivative of y the derivative of f at x with respect to x. dxdy
dxdf
)(xfdxd
dx does not mean d times x !
dy does not mean d times y !
dydx does not mean !dy dx
(except when it is convenient to think of it as division.)
dfdx
does not mean !df dx
(except when it is convenient to think of it as division.)
(except when it is convenient to treat it that way.)
d f xdx
does not mean times !ddx
f x
Constant Rule
If f(x) = 4 If f (x) = π
If the derivative of a function is its slope, then for a constant function, the derivative must be zero.
examples: 3y 0y then f ’(x) = 0 then f ’(x) = 0
Power Rule
examples: 4f x x
34f x x
8y x
78y x
Power Rule Examples
Example 1: Given f(x) = 3x2, find f’(x)
Example 2: Find the first derivative given f(x) = 8x
Example 3: Find the first derivative given f(x) = x6
Example 4: Given f(x) = 5x, find f’(x)
Example 5: Given f(x) = , find f’(x)
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1x 3
€
f '(x) =−3x 4
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f '(x) = 6x
€
f '(x) = 8
€
f '(x) = 6x 5
€
f '(x) = 5
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f (x) = x −3
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f '(x) = −3x−4
Sum or Difference Rule
(Each term is treated separately)
4 12y x x 34 12y x
4 22 2y x x
34 4dy x xdx
EXAMPLES:
Sum/Difference Examples
EX 1: Find f’(x), given:
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f (x) = 5x 4 − 2x 3 − 5x 2 + 8x +11
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f '(x) = 20x 3 − 6x 2 −10x + 8
Sum/Difference Examples
Find p’(t) given
Rewrite p(t): 1
4 12p(t) 12t 6t 5t
13 22
32
p'(t) 48t 3t 5t3 5p'(t) 48t t t
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p(t) =12t 4 − 6 t +5t
Product Rule
2 33 2 5d x x xdx
5 3 32 5 6 15d x x x xdx
5 32 11 15d x x xdx
4 210 33 15x x
2 3x 26 5x 32 5x x 2x
4 2 2 4 26 5 18 15 4 10x x x x x 4 210 33 15x x
One example done two different ways:
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dydx
= f '(x)g(x) + g'(x) f (x)
Product Rule - Example
Let f(x) = (2x + 3)(3x2). Find f’(x)
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f '(x) = (2x + 3)(6x) + (3x 2)(2)
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f '(x) =12x 2 +18x + 6x 2
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f '(x) =18x 2 +18x
Product Rule
Find f’(x) given that
2f (x) x 3 x 5x
1 1
22 21x 3 2x 5 x 5x x2
3 12 25 15x 6x x 152 2
Chain Rule Outside/Inside method of chain rule
insideoutside derivative of outside wrt inside
derivative of inside
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dydx
=ddx
f g(x)( ) = f ' g(x)( ) • g'(x)
Outside/Inside method of chain rule example
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ddx
3x 2 − x +1( )1
3 ⎛ ⎝ ⎜ ⎞
⎠ ⎟= f ' g(x)( ) • g'(x)
€
13
3x 2 − x +1( )−2
3 • (6x −1)
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2x − 13
3x 2 − x +1( )2
3
More examples together:2 71) ( ) (3 5 )f x x x 2 232) ( ) ( 1)f x x
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f '(x) = 7 3x − 5x 2( )6(3 −10x)
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f (x) = x 2−1( )23
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f '(x) =23
x 2 −1( )−1
3(2x)
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f '(x) =
43
x
x 2 −1( )1
3
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3) f (t) =−7
2t − 3( )2€
f '(x) = 3x − 5x 2( )6(21 − 70x)
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f (x) = −7 2t − 3( )−2
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f '(x) =14 2t − 3( )−3(2)
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f '(x) =28
2t − 3( )3
Quotient Rule
3
2
2 53
d x xdx x
2 2 3
22
3 6 5 2 5 2
3
x x x x x
x
EXAMPLE:
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f '(x) =2x 4 + 23x 2 +15 −10x
x 4 + 6x 2 + 9
Quotient Rule Example
Find f’(x) if 2x 1f(x) 4x 3
2
4x 3 (2) 2x 1 44x 3
210
4x 3
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10
16x 2 + 24 x + 9
1
2 2 2( ) 1f x x x 2 2( ) 1f x x x
1 1
2 2 2 22 2( ) 1 1d df x x x x xdx dx
1 1
2 2 22 21( ) 1 ( 2 ) 1 22
f x x x x x x
132 2
12 2
( ) 1 2
1
xf x x x
x
1 12 22 23 3 2 3 3
1 1 1 12 2 2 22 2 2 2
1 2 1 (1 )2 2 2( )
1 1 1 1
x x xx x x x x x xf x
x x x x
3
12 2
3 2( )
1
x xf x
x
3
23 1( )
3xf x
x
2
2 23 1 3 1( ) 3
3 3x d xf x
dxx x
2 2
2 22
3 1 ( 3)3 (3 1)(2 )33 3
x x x xx x
2 2 2
2 22
3 1 (3 9) (6 2 )33 3
x x x xx x
2 2 2
2 22
2 2
42
3(3 1) ( 3 2 9)3 1 3 9 6 233 3 3
x x x xx x
x x x
x
Quotient rule
Product & Quotient Rules
Find
2
27x 9 3 4x (5) (5x 1)( 4) (3 11x 20x )(7)
(7x 9)
x
3 4x 5x 1D 7x 9
x x2
7x 9 D 3 4x 5x 1 3 4x 5x 1 D 7x 9(7x 9)
22
140x 360x 120(7x 9)
Applications
Marginal variables can be cost, revenue, and/or profit. Marginal refers to rates of change.
Since the derivative gives the rate of change of a function, we find the derivative.
Application Example
The total cost in hundreds of dollars to produce x thousand barrels of a beverage is given by
C(x) = 4x2 + 100x + 500Find the marginal cost for x = 5
C’(x) = 8x + 100; C’(5) = 140
Example Continued
After 5,000 barrels have been produced, the cost to produce 1,000 more barrels will be approximately $14,000
The actual cost will be C(6) – C(5): 144 or $14,400
4 22 2y x x
First derivative (slope) is zero
at:
0, 1, 1x
34 4dy x xdx