Posted by Angela on .
find the domains of the following functions:
a) f(x)=x^20
b) g(x)=1/(x3)
c) h(x)=1/(4x^2=21x18)
d) k(x)=sqrt (4x^221x18)
e) p(x)=1/sqrt(4x^221x18)

Pre Cal 
Reiny,
a)  anything goes
b)  anything except x=3
c) we need factors of
4x^2  21x  18
= (x  6)(4x + 3)
so x ≠6 or x ≠ 3/4
d) Now the number inside the √ cannot be negative.
so x ≤ 3/4 or x ≥ 6
e) not the number inside cannot be zero or negative.
you do that one, let me know what you got. 
Pre Cal 
Angela,
isn't it the same as d, because the domain is looked at in the demoninatior?

Pre Cal 
Reiny,
no,
in d) the √ was a numerator while in e) it is now a denominator.
So now we also have to worry about division by zero.
btw, I just noticed a typo which probably caused confusion.
e) should have said:
" e) note that the number inside cannot be zero or negative. "
Of course the result is zero when x=6 or x=3/4, which we cannot have
so just make it : x < 3/4 OR x> 6 
Pre Cal 
Angela,
and x<3/4 or x>6 is the answer?

Pre Cal 
Reiny,
If you understood what I worked for you, you should have realized that I missed the negative sign in x<3/4 as a typo.
so .......
x < 3/4 OR x > 6 
Pre Cal 
Angela,
Oops. sorry i was distracted while writing and forgot to put the negitive.

Pre Cal 
Dalidah,
this is wrong