State the domain of the function and the domain of its derivative

Click For Summary

Discussion Overview

The discussion revolves around finding the derivatives of various functions and determining the domains of those functions and their derivatives. The scope includes mathematical reasoning and application of differentiation rules such as the power rule and quotient rule.

Discussion Character

  • Mathematical reasoning
  • Homework-related
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Participants present several functions for which they seek derivatives and domains, including f(x) = x + √x, f(x) = (3 + x) / (1 - 3x), f(x) = (x^2 + 1) / (x - 2), and f(x) = √3x + 1.
  • One participant claims to have derived the first function incorrectly, stating that x + √x is equal to x^{1/2} and then incorrectly asserting the derivative as x^{3/2}.
  • Another participant corrects the first claim, emphasizing that the derivative of x is 1 and questioning the derivative of √x.
  • For the second function, a participant confirms their derivative calculation as correct, while another expresses uncertainty about applying the quotient rule for the third function.
  • Discussion on the fourth function involves confusion over the expression and its derivative, with participants debating the correct interpretation of the square root and the application of the chain rule.
  • One participant admits to not knowing the derivative of √x and seeks clarification on the power rule for differentiation.

Areas of Agreement / Disagreement

There is no consensus on the correct derivatives or domains of the functions presented. Participants express differing views on the calculations and interpretations of the functions, leading to some confusion and corrections without a clear resolution.

Contextual Notes

Participants' understanding of the power rule and the application of the quotient rule appears to vary, leading to uncertainty in derivative calculations. There are also ambiguities in the interpretation of the fourth function, which may affect the discussion of its derivative.

bballj228
Messages
5
Reaction score
0
Find the derivative. State the domain of the function and the domain of its derivative.

f(x) = x + √x

f(x) = (3 + x) / 1-3x

Find F'(a)

f(x) = (x^2 + 1) / (x - 2)

f(x) = √3x + 1
 
Physics news on Phys.org
And your work so far...?
 


For the first one i got up to x + √x = x^1/2 = x^3/2

2nd one 1(1-3x) - (-3)(3 + x) all over (1-3x)^2 = 10 / (1 - 3x) ^2

3rd one i know its the quotient rule but not sure where to go with this one

For the fourth i tried the chain rule

√3x + 1 = 3x^1/2 + 1 = 1/2(3x)^1/2
 


bballj228 said:
For the first one i got up to x + √x = x^1/2 = x^3/2
? No, x+ \sqrt{x} is NOT equal to x^{1/2}= \sqrt{x} and NEITHER of those is equal to x^{1/2}. Did you mean that \sqrt{x}= x^{1/2}? And that the derivative is x^{3/2}? That last is not correct, either. Surely, you know what the derivative of x= x1 is 1? And what is the derivative of \sqrt{x}= x^{1/2}?

2nd one 1(1-3x) - (-3)(3 + x) all over (1-3x)^2 = 10 / (1 - 3x) ^2
Yes, that is correct!

3rd one i know its the quotient rule but not sure where to go with this one
USE the quotient rule of course! What is (x2+ 1)' ? What is (x- 2)'? Do it just like you did number 2.

For the fourth i tried the chain rule

√3x + 1 = 3x^1/2 + 1 = 1/2(3x)^1/2

Is that √(3)x+ 1, √(3x)+ 1, or √(3x+1)? In any case, none if those is equal to 3x^(1/2)+ 1.

The derivative of √(3) x+ 1 should be trivial. √(3x)+ 1 can be done as √(3)x^(1/2)+ 1, and √(3x+1) should be done using the chain rule: √(3x+1)= √u with u= 3x+1:
(√(3x+1))'= (du^(1/2)/du)(d(3x+1)/dx).
 


HallsofIvy said:
? No, x+ \sqrt{x} is NOT equal to x^{1/2}= \sqrt{x} and NEITHER of those is equal to x^{1/2}. Did you mean that \sqrt{x}= x^{1/2}? And that the derivative is x^{3/2}? That last is not correct, either. Surely, you know what the derivative of x= x1 is 1? And what is the derivative of \sqrt{x}= x^{1/2}?

No, I don't know actually.
 


Use the power rule for differentiation. What is the derivative of x^n? Just apply it to x^1/2.
 

Similar threads

  • · Replies 11 ·
Replies
11
Views
2K
  • · Replies 11 ·
Replies
11
Views
2K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 15 ·
Replies
15
Views
2K
  • · Replies 3 ·
Replies
3
Views
1K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 12 ·
Replies
12
Views
2K
  • · Replies 7 ·
Replies
7
Views
2K
  • · Replies 5 ·
Replies
5
Views
2K
  • · Replies 5 ·
Replies
5
Views
2K