Monday, January 4, 2016

What is the domain of definition of the function f given by f(x)=square root (ln^2x-3lnx+2) ?

The domain of a function f(x) is the set of values of x
for which the value of f(x) is real and defined.


For the
function f(x)= , firstly (ln^2x-3lnx+2) cannot be negative as the
square root of a negative number is a complex number.


This
gives:



ln x + 2 >= 0



>= 0



0


For this to be true either both of the terms in the
product should be positive or both of them should be
negative.


ln x - 1 >= 0 and ln x - 2 >=
0


ln x >= 1 and ln x >=
2


x >= e^1 and x >=
e^2


This is true for x >=
e^2


ln x - 1 < 0 and ln x - 2 <
0


ln x < 1 and ln x
<2


x < e and x <
e^2


As the logarithm is defined only for positive numbers 0
< x < e


The domain of the given function is

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