Finding Domain for Rational Functions :
Here we are going to see how to find domain for rational functions.
The domain of a rational function includes all real numbers except those that cause the denominator to equal zero.
Question 1 :
Find the domain of each of the following real values functions.
f(x) = (x - 1)/(x - 3)
Solution :
Domain means set of all possible values of x. To get the values for which the function be undefined, we have to equate the denominator to 0.
x - 3 = 0
x = 3
Clearly, for the value x = 3 the function will become undefined. So, the domain is set of all real numbers except 3.
Hence R - {3} is the domain of the given function.
(ii) f(x) = (2x - 3)/(x2 - 3x + 2)
Solution :
In order to find domain, let us equate the denominator equal to 0.
x2 - 3x + 2 = 0
(x - 1) (x - 2) = 0
x = 1 and x = 2
Hence R - {1, 2} is the domain of the given function.
(iii) √(x - 2)
Solution :
Domain for the radical function means, the values we choose for x must satisfy the condition f(x) ≥ 0
Note : If the radical function is in the denominator, then it must satisfy the condition f(x) > 0.
x - 2 ≥ 0
x ≥ 2
Hence the required domain is [2, ∞).
(iv) Find the domain of the function f(x) defined by f(x) = √(4 - x) + (1/√(x2 - 1))
Solution :
f(x) = √(4 - x) + (1/√(x2 - 1))
4 - x ≥ 0 x ≥ 4 |
(x2 - 1) > 0 (x + 1) (x - 1) > 0 x > -1 and x > 1 x < -1 and x > 1 |
By selecting a value lesser than -1, √(4-x) and √(x2-1) will become greater than 0.
By selecting a value greater than 1, √(x2-1) will become greater than 0. By choosing a value greater than 4, √(4-x) will become lesser than 0.
By combining the intervals, we get
Domain (f) = (-∞, -1) U (1, 4]
(v) (2x + 1)/(x2 - 9)
Solution :
f(x) = (2x + 1)/(x2 - 9)
f(x) = (2x + 1)/(x + 3)(x - 3)
(x + 3)(x - 3) = 0
x = -3 and x = 3
Domain of f(x) is R - [-3, 3].
After having gone through the stuff given above, we hope that the students would have understood "Finding Domain for Rational Functions".
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