Question

How to find the max of this graph using derivatives? 4x^3-29x^2+93.5 0 12 years ago

Answer 1

take the derivative. What do you get?

Answer 2

12x^2-78x+93.5

Answer 3

Not exactly.. what is the derivative of a constant term?

Answer 4

mhm what do you mean by thatexactly?

Answer 5

isn tit just nx^n-1

Answer 6

Oh shoot I did a mistake ont he equation at first

Answer 7

4x^3-29x^2+93.5x<---

Answer 8

Ah, ok that's more like it.

Answer 9

ok

Answer 10

Now solve the following equation:
12x^2-78x+93.5=0

Answer 11

What do you get when solving for x?

Answer 12

-1.29

Answer 13

Only one solution?

Answer 14

and 0

Answer 15

1.5 and 4.9

Answer 16

sorry those are the answers

Answer 17

so what are the xs that u found?

Answer 18

1.5 and 4.9

Answer 19

Okay, so you have:
0<x<4.25
and x = 1.5 and x=4.9
Plug in each of these values in here:
y=4x^3-29x^2+93.5x and find what y is.
The biggest y value is your max.

Answer 20

cool okay

Answer 21

but I am getting decimal values..

Answer 22

round them..

Answer 23

no but so I found the max of the graph of the original function and got (2.125,61) as the max

Answer 24

but now I am getting values like .342

Answer 25

Sorry, I had a long day at work and am falling asleep here, so @Luigi0210 can you help her out and see what she's doing wrong?

Answer 26

ok

Answer 27

@Luigi0210 u there?

Answer 28

12x^2-78x+93.5

Answer 29

Sorry, Ill be corrected here in a minute. Hope I dont cause any confusion.

Answer 30

butterflyprincess Your first derivative is not correct.

Do it one term at a time.

What is derivative of 4x^3 ?

Answer 31

12x^2?

Answer 32

Yes. What is the derivative of -29x^2 ?

Answer 33

-59x

Answer 34

No. You can try this first. What is the derivative of just x^2 ?

Answer 35

2x

Answer 36

Correct. The -29 is a constant. So (-29) times (2x) = ?

Answer 37

-58x

Answer 38

Yes. And the derivative of the third term 93.5 = ?

Answer 39

the equation is : 4x^3-29x^2+93.5x

Answer 40

the der id 12x^2-58x+93.5

Answer 41

**is

Answer 42

No. The third term is a constant. The derivative of a constant is zero.

Answer 43

93.5x=0???

Answer 44

The third term is 93.5 which is a constant. The derivative of a constant is 0.

The problem had 3 terms: 4x^3-29x^2+93.5

You got the derivative of the first part as 12x^2
You got the derivative of the second part as -58x
The derivative of the third part is 0.

So the derivative of the original function is: 12x^2 - 58x

Answer 45

ok...

Answer 46

Equate the derivative to 0 and solve for x

Answer 47

Could you carefully check the question you posted here?

Your original question says: 4x^3-29x^2+93.5

But later in one of your replies you say: 4x^3-29x^2+93.5x (has an x attached to 93.5)

Which is the correct question?