v = u + a t -----eqn.1

v-final velocity

u-initial velocity

a-acceleration

t-time taken

let the velocity of the particle be v` just two seconds before which means t=(n-2) seconds

Since initial velocity=0.

on applying eq.1,

v`=0+a(n-2)

Now,

S = u t + (1/2) a t²

So the displacement in the last two seconds is

here the velocity before two seconds as found above is {(n-2)a} which becomes initial velocity for last 2 seconds and time is 2 seconds because we want displacement for last 2 seconds

S = {a (n-2) } 2 + (½) a (2²)

S = 2 a (n-2) + 2a

S= 2an-2a

S= 2a(n-1) for last two seconds.