4.2 critical points fri dec 11 do now find the derivative of each 1) 2)

4.2 Critical PointsFri Dec 11

Do Now

Find the derivative of each

1)

2)

Test Review

Critical points

• A number a in the domain of a given function f(x) is called a critical point of f(x) if f '(a) = 0 or f ’(x) is undefined at x = a.

• To find a critical point, we find the 1st derivative and set it equal to 0

• Example 1: Find the critical point(s) of the polynomial function f given by f(x) = x 3 - 3x + 5

Calculator to solve equations

• 1) Graph it (y = )

• 2) 2nd -> calc -> zeros

• 3) left bound / right bound– Click to the left and right of the zero– Guess: hit enter near the zero

Using the Solver Function

• Math -> Solver

• Rewrite the equation so it is equal to 0

Solution

• Solution to Example 1.– The first derivative f ' is given by f

'(x) = 3 x 2 - 3– f '(x) is defined for all real numbers. Let us

now solve f '(x) = 0 • 3 x 2 - 3 = 0 = 3(x-1)(x+1) =0• x = 1 or x = -1

– Since x = 1 and x = -1 are in the domain of f they are both critical points.

• Example 2: Find the critical point(s) of the rational function f defined by

f(x) = (x 2 + 7 ) / (x + 3)

• Solution to Example 2.– Note that the domain of f is the set of all real

numbers except -3. – The first derivative of f is given by f

'(x) = [ 2x (x + 3) - (x 2 + 7 )(1) ] / (x + 3) 2 – Simplify to obtain f '(x) = [ x 2 + 6 x - 7 ] / (x + 3) 2 – Solving f '(x) = 0

• x 2 + 6 x - 7 = 0(x + 7)(x - 1) = 0x = -7 or x = 1 • f '(x) is undefined at x = -3 however x = -3 is not included

in the domain of f and cannot be a critical point. • The only criticalpoints of f are x = -7 and x = 1.

• Example 3: Find the critical point(s) of function f defined by

f(x) = (x - 2) 2/3 + 3

• Solution to Example 3.– Note that the domain of f is the set of all

real numbers. – f '(x) = (2/3)(x - 2) -1/3= 2 / [ 3(x - 2) 1/3] – f ’(x) is undefined at x = 2 and since x = 2

is in the domain of f it is a critical point.

You try: Find the critical points

• a) f(x) = 2x 3 - 6 x - 13

• b) f(x) = (x - 3) 3 - 5

• c) f(x) = x 1/3 + 2

• d) f(x) = x / (x + 4)

answers

• A) 1, -1

• B) 3

• C) 0

• D) none

Closure

• Find the critical numbers of

• HW: p.222 #3-17 odds

4.2 Extreme ValuesMon Dec 14

• Do Now

• Find the critical points of each function

• 1)

• 2)

HW Review: p.222 #3-17 odds

• 3) x = 1• 5) x = -3, 6• 7) x = 2• 9) x = -1, 1 • 11) t = 3, -1• 13) x = -1, 0, 1, sqrt(2/3), -sqrt(2/3)• 15) npi/2• 17) x = 1/e

Extreme Values

• Extreme values refer to the minimum or maximum value of a function

• There are two types of extreme values:– Absolute extrema: the min or max value of

the entire function– Local extrema: the min or max value of a

piece of a function

Absolute vs Local (pics)

• Absolute extrema may or may not exist

• Local extrema always exist

How to find absolute extrema

• 1) Find all critical points in an interval.

• 2) Test all critical points and endpoints into the original function

• 3) The biggest y is the max

The smallest y is the min

Ex

• Find the extrema of the function on [0,6]

Ex 2

• Find the max of the function on [-1, 2]

Ex 3

• Find the extreme values of the function on [1, 4]

Ex 4

• Find the min and max of the function on [0, 2pi]

You try

• Find the extrema of the given function on the indicated interval

• 1)

• 2)

Closure

• Find the min and max of the function on given interval

• HW: p.223 #1 21 29-41 47 51 55 odds

4.2 Rolle’s TheoremTues Dec 15

• Do Now

• Find any critical points for each function

• 1)

• 2)

HW Review: p.222 #1 21 29-41 47 51 55

• 1) a) 3 b) 6 c) max at 5 d) varies• 21) a) c = 2b) f(0)=f(4)=1

c) max: 1, min: -3 d) max: 1, min: -2• 29) min: (-1, 3), max: (2, 21)• 31) min: (0,0) max: (3, 9)• 33) min: (4, -24) max: (6, 8)• 35) min: (1, 5) max: (2, 28)• 37) min: (2, -128)max: (-2, 128)

39 41 47 51 55

• 39) min: (6, 18.5)max: (5, 26)• 41) min: (1, -1) max: (0,0) (3, 0)• 47) min: (0,0) (pi/2, 0) max: (pi/4, 1/2)• 51) min: (pi/3, -.685) max: (5pi/3, 6.968• 55) min: (1,0) max: (e, .368)

Rolle’s Theorem

• Assume that f(x) is continuous on [a,b] and differentiable on (a,b). If f(a) = f(b), then there exists a number c between a and b such that f’(c) = 0

Ex

• Verify Rolle’s Theorem on [-2, 2]

Practice

• Green book worksheet p.268 #33-41

• 1) Critical points– Differentiate and solve = 0

• 2) Test endpoints and c.p. into original function

Closure

• What is a critical point? How can you tell if a critical point is a local max or min?

• HW: worksheet p.268 #33-41