I would guess that the maximum displacement is sqrt(2) and it would occur at 45 degrees.

So the velocity at that point must be zero.

But you didn't want me to guess did you?

so differentiate.

V(t) = cos(t) - sin(t)

Evaluate at pi() / 4 ( 45 degrees)

but cos(pi)/ 4 = sin(pi()/4) = sqrt(2) / 2

hence v(pi()/4) = sqrt(2)/2 - sqrt(2)/2 = 0

v(t) = ds/dt = cost - sint = cos(pi()/4) - sin(pi()/4) = 0 it's instantaneously standing still. ANS.