Policy on Outputting Irrationals as Fractions

There's consensus that answering with fractions is allowable for decimals that can be expressed as fractions. But what about irrational numbers? Can they be expressed as a rational representation of the corresponding decimal approximation?

Examples:

$$\\sqrt{2}\$$ can be approximated as $$\1.4142135623730951\$$, and that's fine because we've established that questions need to establish accuracy. But is approximating it as something like $$\\frac{6369051672525773}{4503599627370496}\$$ or $$\\frac{665857}{470832}\$$ allowable?

$$\\pi\$$ is approximately $$\3.1415926535897\$$, and can be represented by something like $$\\frac{3126535}{995207}\$$ or $$\\frac{884279719003555}{281474976710656}\$$, but is that valid?

Essentially, can fractions be used to approximate irrationals?