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An expression is well-defined if you can compute its value without any illegal operations. Examples of expressions that are not well-defined include 1/0 and \sqrt{-10}. For what values of x is the expression\frac{\sqrt{x + 1} + \sqrt{1 - x}}{\sqrt{x}}well-defined? 

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 Dec 14, 2014

Best Answer 

 #1
avatar+23254 
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Taking the parts individually:  

√(x + 1) is well-defined when  x + 1 ≥ 0   --->   x ≥ -1                                    (x + 1 must be zero or positive)

√(1 - x) is well-defined when  1 - x ≥ 0   --->   -x ≥ -1   --->   x ≤ 1                (1 - x must be zero or positive)

√(x) is well-defined when x > 0                    (x can't be 0 because it is in the denominator)

Since  x > 0  and  x ≥ -1  --->   x > 0

x > 0  and  x ≤ 1    --->     (0, 1]

 Dec 15, 2014
 #1
avatar+23254 
+7
Best Answer

Taking the parts individually:  

√(x + 1) is well-defined when  x + 1 ≥ 0   --->   x ≥ -1                                    (x + 1 must be zero or positive)

√(1 - x) is well-defined when  1 - x ≥ 0   --->   -x ≥ -1   --->   x ≤ 1                (1 - x must be zero or positive)

√(x) is well-defined when x > 0                    (x can't be 0 because it is in the denominator)

Since  x > 0  and  x ≥ -1  --->   x > 0

x > 0  and  x ≤ 1    --->     (0, 1]

geno3141 Dec 15, 2014

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