### 3.1.2 Symbolic constants

Standard constants in Xcas are built-in symbols, given in Table 3.1.

> Symbol | Value
> e (or %e) | the number e1
> pi (or %pi) | the number π
> infinity | unsigned ∞
> +infinity (or inf) | +∞
> -infinity (or -inf) | −∞
> i (or %i) | the complex number 0+1·i
> euler_gamma | Euler’s constant γ:=limn→∞(∑k=1n1/k−ln(n))

> Table 3.1: Symbolic constants in Xcas

Since these numbers cannot be written exactly as standard decimal numbers, they are necessarily left unevaluated in exact results (see Section 2.5.4).

2*pi

2π |  |  |  |  |  |  |  |  |  |

2.0*pi

6.28318530718 |  |  |  |  |  |  |  |  |  |

You can also use evalf (see Section 7.3.1), for example, to approximate one of the real-valued constants to as many decimal places as you want.

evalf(pi,50)

3.1415926535897932384626433832795028841971693993751 |  |  |  |  |  |  |  |  |  |