Arcseconds mean angular distance, whereas parsecs are for linear distance. They are not directly interconvertible, but if a star has a parallax of 1 arcsecond, it is at a distance of 1 parsec. The relationship is the reciprocal of the parallax. So 1/0.75 = 1 1/3 parsec.
The larger the parallax, the smaller the distance, so there is an inverse relationship, not a direct one as the first answerer suggested.
A parsec is 3.26 light years, so 1 1/3 parsec = 4.347 lightyears.
These are two totally different systems of units, measuring totally different thungs. Arc seconds measure angles while parsecs measure distances in space.
You don't. Arcsecond is a unit of angular measurement, while a parsec is a unit of distance. However, when observed from the distance of 1 AU, 1 arcsecond equals 1 parsec.
Parsec is a contraction of "parallax of one arc second," so if an object is observed to shift 1 arc second at an interval of 1 A.U., it is one pc away.
The exact formula for distance in A.U. is
D = 1/tan a
where a is the shift. In radians, since tan a = a for very small values, you can just divide 1 A.U. by the shift. Multiply by pi/6.48E5 to convert seconds to radians.
1/tan (.75 pi/6.48E5) = 275000 A.U. or 4.3 light years.