Given the equation of motion is
y=sinωt+cosωt...(1)
Simplify equation (1) to obtain the standard form:
y==2(sinωtcos4π+cosωtsin4π)2sin(ωt+4π)...(2)
Comparing equation (2) with standard equation of SHM y=Asin(ωt+ϕ), we get amplitude of the given oscillation as 2.