Why cant I do this? (Regarding finding domain of function)

In summary, the conversation discusses the domain of a function and how to determine it using inequalities. There is a mistake in the work shown, where the person incorrectly subtracts 2 from both sides instead of dividing both sides by 2. The domain for the function will be all numbers that satisfy both inequalities given.
  • #1
nukeman
655
0

Homework Statement



Problem:

http://archives.math.utk.edu/visual.calculus/0/domain.1/f6.gif

Homework Equations


The Attempt at a Solution



Look at the pic, and tell me again why I can't do this:

http://i47.tinypic.com/bhadsj.jpg
 
Last edited by a moderator:
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  • #2
-4x +4 is not x

Also be careful with the direction your inequality sign is supposed to point if you start dividing by negatives.
 
  • #3
In addition to what aftershock said, you are missing something else. For f(x) to be defined, it must be true that 9 - 4x ≥ 0 AND 2x - 1 > 0. The domain for this function will be all of the numbers that satisfy both inequalities.

Also, you have a mistake in this work, similar to the one that aftershock pointed out.
2x - 1 > 0
2x > 1 (OK, so far)
Then you subtract 2 from both sides. What's wrong with that is that 2x - 2 ≠ x. To isolate x, divide both sides by 2.
 

1. Why is finding the domain of a function important?

Finding the domain of a function is important because it helps determine the set of values for which the function is defined. This information is crucial in understanding the behavior and limitations of a function.

2. What are the common types of restrictions for a function's domain?

The most common types of restrictions for a function's domain include division by zero, taking the square root of a negative number, and taking the logarithm of a non-positive number. These restrictions are important to identify in order to accurately determine the domain of a function.

3. How can I determine the domain of a function algebraically?

In order to determine the domain of a function algebraically, you must identify any potential restrictions and exclude those values from the domain. This can be done by factoring the function and looking for values that would result in a restriction, or by analyzing the function's equation and identifying any potential restrictions.

4. Can the domain of a function change?

Yes, the domain of a function can change depending on the context or restrictions placed on the function. For example, a function may have a different domain when considering real numbers versus complex numbers, or when taking into account certain limitations or conditions.

5. What are some strategies for finding the domain of a function?

Some strategies for finding the domain of a function include graphing the function and identifying any gaps or discontinuities, using the definition of the function to determine any restrictions, and applying algebraic techniques to identify potential restrictions. It is also important to keep in mind any specific context or limitations that may affect the domain of the function.

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