Question

On which of the following intervals is the function f(x) = 4 cos(2x - π) decreasing?

Answer 1

@rishavraj do you know this?

Answer 2

@tejasvir

Answer 3

@rishavraj

Answer 4

Find f'(x)
Find the interval where f'(x) is negative. That will be the interval where f(x) is decreasing.

Answer 5

@aum is the answer C?

Answer 6

can you also help on this

For an angle Θ with the point (15, -8) on its terminating side, what is the value of cosine?

Answer 7

How did you arrive at C for the first one? Show the work and I can tell you if it is correct or not.

Answer 8

someone just messaged me and told me the answer was C

Answer 9

Sorry, I can't give out answers. Try the method suggested in my first reply.

Answer 10

okay can you help me with this second question then? @aum

Answer 11

For an angle Θ with the point (15, -8) on its terminating side, what is the value of cosine?

I thought it'd be 15, because that's cosine but im not sure

Answer 12

okay so it'd be 15 / hypotenuse

Answer 13

Since it is in the fourth quadrant, cosine will be positive.

Find the length of OP. cos(t) = adjacent /hypotenuse = 15 / OP = ?

Answer 14

15 / 17?

Answer 15

yes. 15/17.03 = 0.8808

Answer 16

wait, but the answer choices don't have that

Answer 17

What are the choices?

Answer 18

the choices are

-8/15

15 / 18

-8

15

Answer 19

any ideas??

Answer 20

I think the choices are wrong. The second choice should have been 15/17.

Answer 21

are you sure? maybe the answer is just 15?

Answer 22

cosine of any angle can never be greater than +1 or less than -1.

Answer 23

but how can the choices be wrong? could it be we're doing it wrong?

Answer 24

Can you copy and paste the exact question?

Answer 25

Wait it was a -8, maybe that's why

Answer 26

The last link does not refer to the question we are discussing.

Answer 27

I'm sorry, wrong one, give me one second

Answer 28

You can quickly rule out the last two choices because \(\large -1 \le \cos(\theta) \le 1\).

You can rule out the first choice because the point (15, -8) lies in the fourth quadrant where cosine is positive.

That leaves with just choice 2 except it should be 15/17 and not 15/18.
(sometimes there are typos in books and notes).

Answer 29

Just choose choice B and most probably it will accept the answer as correct even though there is a typo.

Answer 30

OKay thank you

Answer 31

@aum ONE LAST ONE I PROMISE

Answer 32

A heated piece of metal cools according to the function c(x) = (.5)x - 7, where x is measured in hours. A device is added that aids in cooling according to the function h(x) = -x - 2. What will be the temperature of the metal after 2 hours?

Answer 33

Choices:

-4° Celsius
28° Celsius
32° Celsius
38° Celsius

Answer 34

c(x) = (.5)^(x-7)

Answer 35

For the first question you can look at this graph and figure out in which interval f(x) = 4 cos(2x - π) is decreasing: http://www.wolframalpha.com/input/?i=plot++4cos%282x-pi%29%2C+ [0%2C+2pi]

Answer 36

I figured that out, can you help me on this new one? @aum please I'm in a huge rush now

Answer 37

Find c(2) and h(2) and add them up.

Answer 38

I tried but when you plug in 2 for c(x) it comes out to be like 2?

Answer 39

.25**

Answer 40

What is the initial temperature of the heated metal?

Answer 41

Basically I just need help finding c(2)

Answer 42

It doesn't say.... lol

Answer 43

Is c(x) = (.5)x - 7 or (.5)^x - 7 (Is x an exponent?)

Answer 44

(x - 7) is the full exponent

Answer 45

Then use parenthesis to group items and ^ to denote exponent.
c(x) = (0.5)^(x-7)
x = 2
c(2) = 0.5^(-5) = 32

h(x) = -x - 2
h(2) = -2 -2 = -4

32 + (-4) = 28

Answer 46

so 28 is the answer??

Answer 47

If it is not clear, (0.5)^(-5) = (1/2)^(-5) = (2/1)^(+5) = 32.

Yes, 28 degrees Celsius is the answer.

Answer 48

Thank you so much. Looking over my test, i actually have one more question. You don't have to answer but I'd appreciate if you checked my work

Answer 49

A coach wants to know if football players who warm up before a game will score more points than those who don't warm up. He will break the team up into two groups and make sure each player gets equal time on the field. He will then count how many points each player makes during the game. What statistic should he study?

Answer 50

The mean number of points earned by each player
The mean number of points earned by each group
The standard deviation of the number of points earned by each player
The standard deviation of the number of points earned by each group

Answer 51

I put D

Answer 52

@aum

Answer 53

I would go with B but I am not sure.

For the first question, the function f(x) = 4 cos(2x - π) is decreasing in the interval x = pi/2 and x = pi.

Answer 54

are you 100% sure? someone messaged me and said it was decreasing from pi to 3 pi /2?

@aum

Answer 55

yes.