Question

can anyone help me with calculus

Answer 1

It's possible. The business half is pretty weak up in here, but there are a bunch of calculus ballers hangin' around.

Answer 2

let f(x)=2x cubed-4x find f'(-2) f'(0) f'(2)

Answer 3

\[f(x) = 2x^3-4x\]

Answer 4

Is that right?

Answer 5

yes

Answer 6

Alright, let's start with the basics, my little Grap buddy.
Power rule!
When we derive something that is just a power of x, maybe with a coefficient also, we have a really simple rule for what the result is.
First, you take the exponent and multiply that with the coefficient to get your new coefficient.
Next, you subtract one from your exponent to get your new exponent.
Done. Super simple.

Answer 7

So here's a quick example:
\[f(x) = 6x^5\]
\[f'(x) = 6*5x^{5-1} = 30x^4\]

Answer 8

Understand? Ask me questions.
Try this simple one. What's the derivative of
3x^3

Answer 9

I understand that but the question involves the f'(-2) and f'(0) f' (2)

Answer 10

Okay, so if you understand the differentiating part, then you know the hard part of the problem.

Answer 11

Basically, all we have to do is differentiate f(x) to get f'(x)
and then, since they are asking me f'(-2), I just plug in -2 and solve.

Answer 12

I plugged it in and got 24 but that seems wrong

Answer 13

I believe you took the derivative wrong. What did you get as f'(x)?

Answer 14

24

Answer 15

No no. The FUNCTION. f'(x) should be a function, you know, with x in it and whatnot.

Answer 16

2x cubed-4x

Answer 17

That's f(x). I need to know what you got for f'(x)

Answer 18

I got 24 if f'(-2)

Answer 19

you forgot to include the derivative of -4x then

Answer 20

(2x^3)'(-2) = 24

Answer 21

I am sorry I do not understand

Answer 22

then show us what you get for f'(x)

Answer 23

The answer is 20 but when I plugged in -2 to the function I dd not get the nswer 20

Answer 24

the derivative of (2x^3 - 4x) is not 24

Answer 25

Grap, can we just talk about functions really quick.
YOu have a function f(x). It's a fancy thing that you can plug different values of x into.
You take it's derivative and you get another function f'(x). It's still a fancy thing for plugging x values into.
We're asking you for f'(x), a function, and you're giving us NUMBERS.

Answer 26

i think you only took the derivative of the first part of it; or mistook the -4x as -4.

Answer 27

I do not know how to find the f' function that is whT THEY ARE ASKING ME FOR

Answer 28

how do you get 24 then?

Answer 29

what sorry

Answer 30

I plugged in the -2 into the function and I got -8 sorry

Answer 31

in order to help you out, we have to know how it is that you tried to work the problem; otherwise we are just giving out an answer that has no study value

Answer 32

derivatives follow a few basic principles that can be adhered to; but they have to be memorized to be useful :)

Answer 33

Grap, I think it would be helpful for you to watch me work an example problem.

The problem is:
f(x) = 5x^3, find f'(1), f'(2), f'(3)

Okay, so the first thing to notice is that they are asking for f'(1), not f(1). Do you see the difference?

Answer 34

yes

Answer 35

If it was f(1), I would plug 1 into f(x)
but since it's asking for f'(1), I need to plug 1 into f'(x)

f'(x) is a different function from f(x)

Answer 36

ok

Answer 37

But we don't have the function f'(x). So our first step is to GET THAT FUNCTION. How do we get f'(x)? Well, f'(x) means the derivative of f(x), so we will take the derivative.

Answer 38

f(x) = 5x^3
To take the derivative of that, we follow our derivative rule. Multiply by the power, then take the power down by 1.
5*3 = 15, so that's the new coefficient
3-1 = 2 so that's the new power
f'(x) = 15x^2

Answer 39

Make sure you understand that. That is the most important part of the problem. I had f(x). I took the derivative to get f'(x)

Answer 40

Ask me questions.

Answer 41

Ok so what about the -4x

Answer 42

If our function has different terms, we can go through and use the same rule on each one of them.

Answer 43

Here's an example
f(x) = 3x^3 + 5x^2 +2x - 9
f'(x) = 9x^2 +10x +2
I used the power rule on the first 3 parts separately.

Answer 44

And the last part is a constant, so the derivative is 0.

Answer 45

no i mean my first question was f(x) 2x cubed -4x

Answer 46

You have to understand, what I'm doing is called modelling. You watch me work an example, and you see how it's done. Then you can go and do other problems on your own.

Answer 47

i understand that and I did what you did for my problem but I do not get the answer 20 so I want to find out what I did wrong

Answer 48

-_-

Answer 49

Grap, please understand my frustration. I'm telling you that the important part of the problem is finding f'(x) and you constantly ignore that and try to jump to the answer.

Answer 50

I got it

Answer 51

I understand give me a problem

Answer 52

f(x) = 4x^3 +x^2 +9x
What is f'(x)?

Answer 53

12x squared+2x+9

Answer 54

Good. What is f'(-2)?

Answer 55

53

Answer 56

What is f(-2)?

Answer 57

-54

Answer 58

Pretty close. The x^2 would be +4, not -4, so the answer is -46.

Answer 59

In any case, I think you're right. You understand it. Just get a buncha practice with it now.

Answer 60

thank you

Answer 61

My pleasure, buddy! =D