Posted by **Angela** on Sunday, July 24, 2011 at 8:20pm.

find the domains of the following functions:

a) f(x)=x^20

b) g(x)=1/(x-3)

c) h(x)=1/(4x^2=21x-18)

d) k(x)=sqrt (4x^2-21x-18)

e) p(x)=1/sqrt(4x^2-21x-18)

- Pre Cal -
**Reiny**, Sunday, July 24, 2011 at 9:18pm
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**, Sunday, July 24, 2011 at 9:23pm
isn't it the same as d, because the domain is looked at in the demoninatior?

- Pre Cal -
**Reiny**, Sunday, July 24, 2011 at 9:30pm
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**, Sunday, July 24, 2011 at 9:32pm
and x<3/4 or x>6 is the answer?

- Pre Cal -
**Reiny**, Sunday, July 24, 2011 at 9:42pm
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**, Sunday, July 24, 2011 at 9:44pm
Oops. sorry i was distracted while writing and forgot to put the negitive.

- Pre Cal -
**Dalidah**, Tuesday, August 16, 2011 at 4:54pm
this is wrong

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