Question

Choose the value for which 2/a+8 is undefined

Answer 1

If the value is:

$\sf{\frac{2}{a+8}}$

Then it will be undefined when the denominator is equal to 0.

So set the denominator equal to 0

a + 8 = 0
a = -8

So when 

$\huge{\boxed{\bf{a=-8}}}$

then the value will be undefined.

Just a note:

$\sf{\frac{x}{0}=}$ undefined

$\sf{\frac{0}{x}=0}$