The domain of the function fx=1Cx-1 10-3× 10Cx is
{9, 10, 11}
{9, 10, 12}
all natural numbers
{9, 10}
Given function is defined if Cx-1 10>3 10Cx
or 111-x>3x or 4x>33
or x≥9
But 10 ≥ x-1 .and 10≥x so x≤10
∴ x=9, 10