for f(x)=2x+1 state which value of x must be excluded from any domain of f

Answer 1

domain is all real numbers

You'd exclude any numbers that involve division by 0

If f(x) had been 2/x +1, you'd exclude x=0

if f(x) had been 2/(x+1) you'd exclude x=-1

but as written 2x +1, there is no value that's excluded.

Odds are you left out a division sign, "/" between the 2 and x