Differential calculus, derivatives

In summary, the conversation discusses finding the derivative of a function using first principles. The attempt at solving the problem showed a mistake in the calculation, but after correcting it, the correct answer was obtained.
  • #1
DERRAN
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0

Homework Statement



Find f'(x)= 16x - x-2 using first principles.

Homework Equations


x
http://img153.imageshack.us/img153/8403/597137697c1f605c7a43d34qz4.png


The Attempt at a Solution


I used dy/dx and got 2x-3 + 16 but I get something different when I use the formula I attempted several times and I can't get the same answer as the dy/dx.
Please need help!
 
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  • #2
Do you mean "find f'(x) if f(x)= 16x- x-1"? That's quite different from what you say!

If f(x)= 16x- x-2, then f(x+h)= 16(x+h)- (x+ h)-2

f(x+h)- f(x)= 16(x+ h)- 16x - (x+h)-2+ x-2

The first part of that is just 16x+ 16h- 16x= 16h.

The second part is
[tex]-\frac{1}{(x+h)^2}+ \frac{1}{x^2}[/tex]
[tex]= \frac{-x^2}{x^2(x+h)^2}+ \frac{(x+h)^2}{x^2(x+h)^2}[/tex]
[tex]= \frac{-x^2+ x^2+ 2hx+h^2}{x^2(x+h)^2}= \frac{2hx+ h^2}{x^2(x+h)^2}[/tex]
so
[tex]f(x+h)- f(x)= 16h+ \frac{2hx+h^2}{x^2(x+h)^2}[/tex]
Now, what is (f(x+h)- f(x))/h and what is the limit of that as h goes to 0.
 
  • #4
you've lost a square from the denominator for no reason during your calc, they should work
 
  • #5
Thanks sorry about that it works perfectly!
 

Related to Differential calculus, derivatives

1. What is differential calculus?

Differential calculus is a branch of mathematics that deals with the study of rates of change in a function. It involves finding the derivative of a function, which represents the instantaneous rate of change of the function at a specific point.

2. What is a derivative?

A derivative is a mathematical concept that represents the rate of change of a function at a specific point. It is calculated by finding the slope of the tangent line to the function at that point. In other words, it tells us how much a function is changing at a particular point.

3. How is differential calculus used in real life?

Differential calculus has many applications in real life, including in physics, economics, engineering, and even in everyday situations. For example, it can be used to determine the maximum or minimum value of a function, which is useful in optimization problems. It is also used in calculating velocity, acceleration, and other rates of change in physical systems.

4. What are the basic rules for finding derivatives?

There are several rules for finding derivatives, but some of the most basic ones include the power rule, the product rule, and the chain rule. The power rule states that the derivative of a function raised to a constant power is equal to the product of the constant and the function raised to the power minus one. The product rule states that the derivative of a product of two functions is equal to the first function times the derivative of the second function plus the second function times the derivative of the first function. The chain rule is used to find the derivative of a composite function.

5. Can any function have a derivative?

No, not all functions have derivatives. For a function to have a derivative at a specific point, it must be continuous at that point and have a well-defined slope. Functions that have sharp corners, vertical tangent lines, or are not defined at a certain point do not have derivatives at that point.

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