Find the largest possible domain of this rational function!
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Find the largest possible domain of this rational function!

[From: ] [author: ] [Date: 12-04-13] [Hit: ]
since we cannot take the square root of a negative number to get a real result.Restrictions of a rational:Denominator cannot equal 0.In order for this function to be valid, the inside of the radical must be greater than equal to 0, i.e.......
Find the largest possible domain of the function
f(x) = 1/sqrt(4+3x)
Express your answer in interval notation.

Thanks!

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4 + 3x must be > 0
3x > - 4
x > -4/3

So domain is ( -4/3 , infinity)

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As an aside, "largest possible domain" is strange terminology to me; I've always known the domain of a function to be all possible values of x, so prefixing it with "largest possible" sounds redundant to me.

But I digress.

f(x) = 1/sqrt(4 + 3x)

First off, this function has two restrictions.
1) The function has a radical (square root) in it, and
2) The function is a rational (i.e. a fraction).

Restrictions of a radical: Inside of the square root must be greater than or equal to 0, since we cannot take the square root of a negative number to get a real result.
Restrictions of a rational: Denominator cannot equal 0.

In order for this function to be valid, the inside of the radical must be greater than equal to 0, i.e.
4 + 3x >= 0

If we solve this inequality, we get
3x >= -4
x >= -4/3

Next, in order for this function to be valid, the denominator cannot equal 0. So what then makes the denominator _equal_ to 0? If we find this out, we'll know what values x CANNOT be.

sqrt(4 + 3x) = 0. Square both sides to get
4 + 3x = 0
3x = -4
x = -4/3; therefore, x CANNOT equal -4/3.

Combining the two facts:

x >= -4/3 AND x cannot equal -4/3.
Which is the same as saying

x > -4/3

Domain: (-infinity, -4/3)

Or, in set notation,
{x | x > -4/3, for x E R}

"The set of all real numbers x such that x is strictly greater than -4/3."

-
4 + 3x >= 0
3x >= -4
x >= -4/3

So, x is greater than or equal to -4/3 or you could say (-4/3, infinity) in interval notation.

-
sqrt(4+3x)>0
x>-4/3 or x belongs (-4/3, +infinity)
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