How to get rotation matrix from 3d points?

I have 3 3d points and I need to find rotation matrix from these points.

P1(-401.428, 485.929, 772.921)

P2(-21.4433, 475.611, 772.511)

P3(-400.982, 483.56, 403.703)

How could I compute 3x3 rotation matrix? They are orthogonal. And I set P1 as a reference point.

Answer 1

[Shadaab Siddiqie]

All the rotation matrix are orthogonal. To find rotation matrix for each axis please refer rotx. For more information about Matrix rotation refer this link.

[SOONMYUN JANG]

I got it. Thank you!