Can the set of numbers 8,12,4 make a triangle? and if it can, does it make a right triangle

  No

Step-by-step explanation:

The sum of the shorter two lengths is exactly equal to the longer length. The "triangle" made by these segments will look like a line segment of length 12. It will have zero area.

Many authors would tell you this is not a triangle. (Others will tell you it is a triangle—a degenerate case.)

These numbers are an arithmetic sequence. The ratio of lengths is 1 : 2 : 3. The only arithmetic sequence of side lengths that makes a right triangle are those in the ratio 3 : 4 : 5.