Which numbers cannot be used in place of x in the rational expression?

Question

(x+8)/(x2-81)

I reads X+8 over x exponet 2 -81

Thanks 4 the help and I wish I could build my yahoo answers points like you all,lol.

Answer 1

Well this is a rational expression, so you have to comsider that it is undefined if the denominator equals 0. So set the denominator equal to zero, solve for x, and we know what numbers can't be used for x.
x^2-81=0 is a difference of two squares
(x+9)(x-9)=0
x+9=0 or x-9=0
x=-9 or x=9
Therefore possible solutions for x are all real numbers except -9,9.

Answer 2

x= 9
(9+8)/(9^2-81)
=17/(81-81)
=17/0
= infinity


x= -9
(-9+8)/{(-9)^2-81}
= -1/(81-81)
= 17/0
= infinity


x = any irrational number cannot be used either

Answer 3

(x + 8)/(x^2 - 81)
(x + 8)/((x - 9)(x + 9))

x cannot equal 9 or -9

Answer 4

9 and -9. Then the right parenthesis will be equal to 0, and division with zero is illegal.

Answer 5

9 or -9. These would cause division by zero.