The equation ex-x-1=0 has
Only one real root x=0
At least two real roots
Exactly two real roots
Infinitely many real roots
ex=x+1⇒1+x1!+x22!+.....=x+1 ⇒x22!+x33!+....=0 x2=0, x3=0, ....xn=0
Hence, x=0 only one real root.