Derive first law of newton from second law of motion

1st Law states that an object will continue without a change in motion (constant velocity) if there are no outside forces.

2nd Law states that to have an accn, there must be an outside force.
$\sum F=m\cdot a$

If F = 0

$\sum F=m\cdot a$ becomes 
$0=m\cdot a$
$0=a$

And if there is no acceleration, there is no change in motion (1st law).