Question

What is the rate of change for f(x) = −2 cos(4x − 3) on the interval from x = pi / 4 to x = pi / 2?
A. -pi / 16
B. -16 / pi
C. 2 / pi
D. pi / 2

Answer 1

@mathstudent55

Answer 2

@desuoverlord

Answer 3

@precal

Answer 4

just sub and use the slope formula

Answer 5

I have no idea on how to sub

Answer 6

really this is an advance math problem......precal or calculus level

Answer 7

strange, maybe you are in the wrong course

Answer 8

im taking an algebra 2 honors class

Answer 9

still you have sub before
example
f(x)=2x+3 find f(4)

Answer 10

11

Answer 11

see you know how to sub

Answer 12

sub pi/4 into f(x)

Answer 13

4.57079...

Answer 14

no leave in radian

Answer 15

(pi / 2) + 3

Answer 16

so D!

Answer 17

did you do the second substitution?

Answer 18

pi over 4?

Answer 19

what? I got pi / 2

Answer 20

no remember you need to use the slope formula with both of them

Answer 21

so I still need to find 'y'.

Answer 22

[f(π/2)−f(π/4)]/[(π/2)−(π/4) ]

Answer 23

remember difference of y over difference of x, slope formula

Answer 24

1

Answer 25

is that right??

Answer 26

no, I don't think so, is it cos(4x-3) or cos(4x)-3 ?

Answer 27

-2cos(4x - 3)

Answer 28

need to check with my graphing calculator

Answer 29

none are working out, are you sure you wrote the problem correctly?

Answer 30

@bahrom7893 can you double check me?

Answer 31

yes...

Answer 32

What is the rate of change for f(x) = −2 cos (4x − 3) on the interval from x = pi over 4 to x = pi over 2?

Answer 33

(f(x2) - f(x1))/(x2 - x1) should give you the answer

Answer 34

that makes no sense, are you solving for x?

Answer 35

This is also a strangely worded question, do you mean AVERAGE rate of change? The rate of change over that interval is defined using the derivative and is used to show how the function is changing at a specific point. The average rate of change is 4cos(3)~-4, which is what these guys already said.

Answer 36

when I did the pi/2 sub I got
-2cos(4(pi/2)-3)
-2 cos(2pi-3)
can I simplify it anymore?

Answer 37

but she said she is in Algebra II honors, that doesn't make any sense

Answer 38

Algebra II doesn't do derivatives

Answer 39

yeah, I didn't use it, just confirming what the question was, usually you would say average rate of change for this type of question.

Answer 40

this is the final chapter in the class which is all about trig

Answer 41

^^so how would you figure out to answer

Answer 42

are you sure your problem is not -2cos(4x)-3 because it makes a big difference

Answer 43

the orig. problem has no parenthesis

Answer 44

http://i.imgur.com/k5T5d62.png

I have done it via calculator, there is no way it is one of those answers.

Answer 45

I believe it is what I wrote
-2cos(4x)-3
-2cos(4(pi/2))-3
-2 cos2pi -3
-2(0)-3
0-3
-3

Answer 46

could it be B, since there is a neagative , 16 on top, and pi on the bottom?

Answer 47

-2cos(4x)-3
-2cos(4(pi/4))-3
-2 cos(pi )-3
-2(-1)-3
2-3
-1
we don't guess in math

Answer 48

-3--1=-3+1=-2 on top

Answer 49

(pi/2)-(pi/4)
2pi/4 - pi/4
pi/4

Answer 50

-2 over pi/4
-2 times 4/pi
-8/pi

Answer 51

strange none look like that

Answer 52

x2 = B

Answer 53

@sylbot I got what you got earlier with my graphing calculator, see any mistakes on my part

Answer 54

There must be an error in precal's work, I'm getting B as the answer, adjusting for the parenthesis (the -3 is outside) let me work it out tho.
http://i.imgur.com/Tjrb6bK.png
Ignore the bottom.

Answer 55

yes pi over 2 is -5

Answer 56

-4 over pi/4
-4 times 4/pi
-16/pi

Answer 57

thanks so much! do youhave time for one more question

Answer 58

yes it is B
btw the -3 is outside of the ( ) and that does matter

Answer 59

I found the error, precal cos(pi)=1 not zero.

Answer 60

correct its -1 and I found the mistake as well
close this problem and start a new thread

Answer 61

oo0ooooops cos(2pi)=1

Answer 62

believe it is what I wrote
-2cos(4x)-3
-2cos(4(pi/2))-3
-2 cos2pi -3
-2(0)-3
0-3
-3

here it was haha could happen to anyone,
glad you got the help you need in the end.

Answer 63

@sylbot cos (2 pi) is 1
-2(1)-3
-2-3
-5 and this is where I made the mistake
but you were right
thanks for catching it