Derivation of the 1st equation of motion

Consider a body of mass m having a initial velocity u.
Let after time t, its final velocity be v due to an uniform acceleration a.

Now we know that:
Acceleration = Change in velocitytime taken

=> Acceleration = Final velocityInitial velocitytime taken

=> a = vut
=> at=vu

=>  v=u+at
This is the first equation of motion.