# Search:

Type: Posts; User: JeffM

Page 1 of 20 1

1. ## Thread: Is this possible?

by JeffM
Replies
3
Views
52

### You don't tell us what answer you got from the...

You don't tell us what answer you got from the quadratic formula or how you got it. So it is impossible to tell where your train flew off the tracks.

3x^2 - 2x + 7 = 0 \implies x = \dfrac{-\ (-\...

by JeffM
Replies
11
Views
266

Lovely
3. ## Thread: Place value: "The numeral for twenty hundredths is...?"

by JeffM
Replies
5
Views
133

### I do not believe "numeral" means "digit." The...

I do not believe "numeral" means "digit." The Arabic numeral for "twenty" is 20, and the Roman numeral for "twenty" is XX. "Numeral" means a symbol representing a unique number.

"Digit" is a word...
4. ## Thread: serious problem help needed: there are 400 llamas and alpacas in total....

by JeffM
Replies
16
Views
446

### Because our students NEVER post in the wrong...

Because our students NEVER post in the wrong forum!
5. ## Thread: optimisation problem: Maximize area of rect above x-axis, under y=12-x^2

by JeffM
Replies
6
Views
134

### \text {Area of rectangle in first quadrant} =...

\text {Area of rectangle in first quadrant} = a_1.

\text {Area of rectangle in first and second quadrant} = a_2.

a_1 = (x - 0) * (12 - x^2) = 12x - x^3 \implies

\dfrac{da_1}{dx} = 12 - 3x^2...
6. ## Thread: optimisation problem: Maximize area of rect above x-axis, under y=12-x^2

by JeffM
Replies
6
Views
134

### I think what is being asked is whether, to...

I think what is being asked is whether, to compute the maximum area of a rectangle bounded by the x-axis, y-axis, and the given parabola, you can halve the maximum area of a rectangle bounded by the...
7. ## Thread: serious problem help needed: there are 400 llamas and alpacas in total....

by JeffM
Replies
16
Views
446

### Whether mmm's answer is algebra in disguise...

Whether mmm's answer is algebra in disguise depends on how we define algebra. I don't think his answer depends on elementary algebra in its traditional sense. It is more a combination of trial and...
8. ## Thread: Problem w/ induction? How does 1/2k(6k^2 + 3k − 1) + [3(k+1)-1]^2 become...?

by JeffM
Replies
2
Views
85

### \text {Let } u = k + 1 \implies \{3(k + 1) -...

\text {Let } u = k + 1 \implies \{3(k + 1) - 1\}^2 = (3u - 1)^2 = (3u - 1)(3u - 1) =

3u(3u - 1) - 1(3u - 1) = 9u^2 - 3u - 3u + 1 = 9u^ 2 - 6u + 1 \implies

\{3(k + 1) - 1\}^2 = 9(k + 1)^2 - 6(k...
9. ## Thread: Solving for A in terms of B & C

by JeffM
Replies
11
Views
266

### I am going to try again. When you want to...

I am going to try again.

When you want to eliminate fractions from an equation, you multiply both sides by the least common multiple of the denominators. You multiplied both sides by 2, WHICH IS...
10. ## Thread: Solving for A in terms of B & C

by JeffM
Replies
11
Views
266

### NO WONDER YOU ARE CONFUSED. I made an error. My...

NO WONDER YOU ARE CONFUSED. I made an error. My original post made NO SENSE. My abject apologies. I do not have the time to correct myself right now. I shall be back in a little over an hour and try...
11. ## Thread: Least amount of operations to convert an 18th of a second into a 30th.

by JeffM
Replies
12
Views
429

### Formulating questions carefully is frequently far...

Formulating questions carefully is frequently far more than half the battle when answering them.

by JeffM
Replies
12
Views
272

### GREAT question, but I disagree slightly with...

GREAT question, but I disagree slightly with tkhunny's answer on this one.

Let's start with a point of logic. "P or Q" is exactly equivalent to "Q or P." Agree?

What does x = \dfrac{-\ b \pm...
13. ## Thread: Prove truth of circle division theory by 5 equal parts

by JeffM
Replies
2
Views
95

### I cannot read the second picture, too small. ...

I cannot read the second picture, too small.

You have a circle with the origin at O and perpendicular diameters AOB and COD. The midpoint of AO is at E. You construct the right triangle EOD. The...
14. ## Thread: Having trouble simplifying

by JeffM
Replies
4
Views
141

### I now see a much simpler solution based on these...

I now see a much simpler solution based on these two lemmas.

(a + b)^2 - (a - b)^2 = a^2 + 2ab + b^2 - (a^2 - 2ab + b^2) = 4ab.

(c + c^{-1})^2 = c^2 + 2c^{(1-1)} + c^{-2} = c^2 + 2 +...
15. ## Thread: Simple Equity Division: Divorcing couple needs to equalize equity, debt of vehicles

by JeffM
Replies
13
Views
416

### Very likely outcome.

Very likely outcome.
16. ## Thread: Solving for A in terms of B & C

by JeffM
Replies
11
Views
266

### 14 - 6 + 21 - 6 = 8 + 15 = 23. 14 - 6 + 21 - 6...

14 - 6 + 21 - 6 = 8 + 15 = 23.

14 - 6 + 21 - 6 \ne 14 + 21 = 35.

Do you see your major error now? You were to subtract BC twice, which is the same as subtracting twice BC. Instead you cancelled...
17. ## Thread: How to interpret this formula? Sn=C*mediani{medianj|xi−xj|} where C = 1.1926

by JeffM
Replies
5
Views
220

### I have no idea what you are saying. What does...

I have no idea what you are saying. What does median i even mean? Similarly with median j. What is the relevance of n? Is S a sequence or a sum?

If I want the differences between the elements in...
18. ## Thread: Having trouble simplifying

by JeffM
Replies
4
Views
141

Answering your last question first, there is a fussy formatting language available here, but I recommend that students ignore it and concentrate on math. Just write things out in line using grouping...
19. ## Thread: Least amount of operations to convert an 18th of a second into a 30th.

by JeffM
Replies
12
Views
429

### Look. We really want to help you. And some of us...

Look. We really want to help you. And some of us at various times in our career have done things with computers. But to answer a math question, we need to translate the practical problem into...
20. ## Thread: Question about Lagrange multipliers for maximizing a function with two constraints

by JeffM
Replies
13
Views
439

### OK, but did you not say in post # 8 that the...

OK, but did you not say in post # 8 that the factory could only run for 20,000 hours per period and that it took 2 hours to produce one unit of x and only 1 hour to produce one unit of y. In that...

by JeffM
Replies
6
Views
187

### I'd like to thank both Dr. Peterson and ksdhart...

I'd like to thank both Dr. Peterson and ksdhart for their pertinent and extended answers.
22. ## Thread: finding derivative of an inverse function given f(x) = x^5 +3x +6

by JeffM
Replies
7
Views
425

### Bob Ahh I see. Not a problem. I really did...

Bob

Ahh I see. Not a problem. I really did think there might have been something subtle going on.

Thanks for following up.
23. ## Thread: Mathematical No-Man's Land b/t Intuition & Comprehension???

by JeffM
Replies
11
Views
441

### As I said, I am not a mathematician. I merely...

As I said, I am not a mathematician. I merely tutor in the basics that I learned decades ago and used often enough since then to remember well. So I cannot advise on books. I suspect that the...
24. ## Thread: Question about Lagrange multipliers for maximizing a function with two constraints

by JeffM
Replies
13
Views
439

### As I read what you have written, I must assume...

As I read what you have written, I must assume that the objective function is:

c(x, y) = -\ 0.1x^2 + 395x + 100y.

But I see only one relevant constraint, namely 2x + y \le 20,000.

How did...
25. ## Thread: Question about Lagrange multipliers for maximizing a function with two constraints

by JeffM
Replies
13
Views
439

### That is MUCH better. The objective function is...

That is MUCH better.

The objective function is the contribution margin:

c(x, y) = -\ 0.1x^2 + 395x + 100y.

I shall assume that this is correct. Obviously, it is to be maximized. But it is...
Results 1 to 25 of 500
Page 1 of 20 1