The functions have the same frequency and amplitude, but different initial phases

Distance travelled by the mass sideways, $A=2.0 \,cm$

Force constant of the spring, $k=1200\, N m ^{-1}$

Mass, $m=3 \,kg$

Angular frequency of oscillation:

$\omega=\sqrt{\frac{k}{m}}$

$=\sqrt{\frac{1200}{3}}=\sqrt{400}=20 \,rad s ^{-1}$

When the mass is at the mean position, initial phase is $0 .$

Displacement, $x=A \sin \omega t$

$=2 \sin 20 t$

At the maximum stretched position, the mass is toward the extreme right. Hence, the

initial phase is $\frac{\pi}{2}$

Displacement, $x=A \sin \left(\omega t+\frac{\pi}{2}\right)$

$=2 \sin \left(20 t+\frac{\pi}{2}\right)$

$=2 \cos 20 t$

At the maximum compressed position, the mass is toward the extreme left. Hence, the initial phase is $\frac{3 \pi}{2}$

$x=A \sin \left(\omega t+\frac{3 \pi}{2}\right)$

Displacement,

$=2 \sin \left(20 t+\frac{3 \pi}{2}\right)=-2 \cos 20 t$

The functions have the same frequency $\left(\frac{20}{2 \pi} Hz \right)$ and amplitude $(2 \,cm ),$ but different initial phases $\left(0, \frac{\pi}{2}, \frac{3 \pi}{2}\right)$