the right slant and left slant refer to the orientation of the finished stitches, not how you insert your needle to do them.
for the /3 (right slanting triple decrease)
slip 3 stitches individually as if to knit.; insert the left needle from left to right and knit these three stitches together. Return the resulting stitch to the left needle. lift the second stitch on the left needle over the stitch you just returned to left needle and off. move the first stitch back to the right needle.
for the 3\ slip one as if to knit;
knit three together, pass the slipped stitch over.