# Questions and Answers

# Your Questions About X1

Sharon asks…

## What happens when you apply Newtons Method is applied Calculus?

What happens when you apply Newtons Method to F(x)=x^3-5X with an initial guess of **X1**=1? explain this geometrically with a graph.

### Administrator answers:

Basically newtons method is saying that x of n+1 is a better approximation than x of n for the root x of the function f.

When you show this graphically you will have a tangent line to f(x) that is clearly a better approximation of the root.

F n+1 = Xn – F(Xn)/F’(Xn)

or in your case: f n+1 = X1 – F(X1)/F’(X1) *note f prime in denominator

James asks…

## How do I calculate tire pressure of my car?

I’m doing a lab for school and the recommended tire pressure for my car is 32 psi. I had a 1″**x1**” grid and rolled the tire over it getting an area of 42 inches. The weight of th car is 3532 lbs. I received my answer by dividing the weight by the area…is this the correct formula to get the answer? Would I then divide that answer by 4 for all 4 tires?

### Administrator answers:

Yes, weight gives you the normal force. Each tire carries (1/4) of the car weight.

Pressure is force divided by area.

Ptotal=W/42

Pone=W/168=3532/168=21 lb/in^2

Susan asks…

## What good gaming video cards can I install onto a Dell Dimension 3100 computer?

It does not come with a good video card, and thus I need a new one. There are PCI slots, and a PCI-E **x1** slot. Please include links to the video cards you are recommending.

### Administrator answers:

Even if you could put a new card in, that computer is much too old to be brought to life just by a videocard.

You need a new mobo, which means a new cpu, and ram, and possibly a power supply.

Basically a new computer.

Keep that one in tact and use it for something else, like a web browsing computer

i can design you a new computer that you can take the list to your local computer shop and get them to build it, or buy the parts and make it yourself (very easy)

just email me with a price range if you’d like that (remember specify the currency though, I’m in Australia)

Jenny asks…

## Functions of 8 variables with definite expression,how do I find their ranges?

functions f1,f2,f3,f4 of **x1**,x2,x3,x4,x5,x6,x7,x8. The functions have definite expressions.Specifically,f1=**x1***x3+x5*x7,f2=x2*x3+x5*x8,f3=**x1***x4+x6*x7,f4=x2*x4+x6*x8.

The domain of each variable is (0,10).How do I find the global maximum and minimum of each of the four functions?

Preferably with help of mathwares,like MATLAB or Mathematica.

Thank you very much!

### Administrator answers:

Probably using some of the search functions in these mathwares.

In MatLab, I only remember fmincon, which may be too powerful for your purpose, but from it you can find other similar functions and use the appropriate one. These functions only search for minimum. So, to find maximum, negate the functions.

Since you are given the domain, aren’t you finding the local instead of global maximum/minimum?

You may do a dynamic search with 8 loops trying “all” values of each values in the domain (e.g. For x1 = 0:0.01:10). Check if the maximum/minimum corresponds to that you get from the search functions.

Chris asks…

## What kind of screws do I need to put up a wall shelf?

I’m trying to put up a wall shelf that I bought from IKEA. I didn’t realize that different walls required different types of screws. I had bought some #10 **X1**-1/2″ flat head phillips screw at a nearby hardware store, but unfortunately, even when I drill the screw through a stud, the screws fail to hold the shelf in place. I can literally pull the screws out from the wall with my bare hand. Would using “plugs” or “mooring screws” do the job? Thanks.

### Administrator answers:

Yes, or even better are you sure you are hitting the stud? If so, use longer screws…

Richard asks…

## When finding the slope of a line, how do you know which endpoints are y2 and x2?

So the formula for slope of a line is y2-y1/x2-**x1**, but how do you tell which y is y2 and which is y is y1, and which x is x2 and which x is **x1**???

This is probably a really stupid question but I’m confused >.<

### Administrator answers:

The two points are (x1,y1) and (x2,y2) and it doesn’t matter which is point 1 and which is point2.

Carol asks…

## How to find the global maximum (or minimum) of a multivariable function?

I have a function f(**x1**,x2,…,xi) and want to find the global maximum. How can I do it?

Thanks!

### Administrator answers:

Compute their derivatives and set it equal to 0, obtain the corresponding x value. Then compute the value of the function[f(x)] at the respective x coordinates and also compute the values of each function at the boundary of the domain (if there is any). Then, compare all the values and see which one is the largest.

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