# Sorry another math question again

• Jan 31st 2008, 08:23 PM
Girlaaaaaaaa
Sorry another math question again
Find the domain of f(x)= 3/((square root)x-7(end square root)) Write in interval notation. How would that be done?

Also what would be the domains of:
(x^2)-13*x+x+8
(x^2)-13*x-(x+8)
[(x^2)-13*x]*(x+8)

and also the domain of f+g
f-g
fg
given that f(x)=(square root)8+x(end square root) and g(x)=(square root)8-x(end square root)
• Jan 31st 2008, 09:03 PM
Jhevon
Quote:

Originally Posted by Girlaaaaaaaa
Find the domain of f(x)= 3/((square root)x-7(end square root)) Write in interval notation. How would that be done?

remember the domain of a function is the set of all input values that we can plug in, in this case, that is the x-values. so what x-values CAN'T we plug in? the domain is all x's except those.

$\displaystyle f(x) = \frac 3{\sqrt{x - 7}}$

first thing we notice, this is a fraction, so the denominator cannot be zero. so one x we cannot be is the one that makes the denominator zero. now for the square root, what is being square rooted must be greater than or equal to zero. the first condition prevents us from being 0, so the domain is given by all real x such that x - 7 > 0. so what is your solution? can you write it in interval form?

Quote:

Also what would be the domains of:
(x^2)-13*x+x+8
(x^2)-13*x-(x+8)
[(x^2)-13*x]*(x+8)
these are all polynomials. their domains are all real x

Quote:

and also the domain of f+g
f-g
fg
given that f(x)=(square root)8+x(end square root) and g(x)=(square root)8-x(end square root)
consider what i said on the first problem and try this