find the equation of the plane that goes through (1,2,-1) and making equal angles with the positive directions of the coordinate axes

Hello, ramzouzy!
Find the equation of the plane that goes through (1,2,-1) and
makes equal angles with the positive directions of the coordinate axes
This plane is tilted so there is an equilateral triangle in the first octant.
. . It has normal vector: .
Hence, its equation has the form: .
Since (1,2,-1) is on the plane: .
Therefore: .