Add mathutil package and constants

Introduce a new package for math utilities, including an Add function
and Euler's number. Also, add constants for Celsius conversion and basic
arithmetic.

README.md

@@ -3,3 +3,4 @@
 https://www.youtube.com/watch?v=ID9NZ88JeOE
 
 1. (00:04:58) Package
+2. (00:15:14) Func

go.mod

@@ -0,0 +1,3 @@
+module curso-goland
+
+go 1.25.0

main.go

@@ -2,8 +2,40 @@ package main
 
 import (
 	"fmt"
+	"curso-goland/mathutil"
+	"math"
+)
+
+const GrauCelsius = 273.15
+
+const (
+	A = 1
+	B = 2
 )
 
 func main() {
 	fmt.Println("Hello, World!")
+
+	fmt.Println(mathutil.Add(1, 2))
+
+	fmt.Println(math.Sqrt(144))
+
+	var x int = 10
+	x = x + 1
+	fmt.Println(x)
+
+	var a, b int = 1, 2
+	c := a + b
+	fmt.Println(c)
+
+	nombre, edad := "Juan", 30
+	fmt.Println(nombre, edad)
+
+	fmt.Println(mathutil.EulersNumber)
+
+	fmt.Println(math.Pi)
+
+	fmt.Println(GrauCelsius)
+
+	fmt.Println(A + B)
 }

mathutil/mathutil.go

@@ -0,0 +1,7 @@
+package mathutil
+
+var EulersNumber float64 = 2.7182818284590452353602874713526624977572470936999595749669676277240766303535475945713821785251664274
+
+func Add(a, b int) int {
+	return a + b
+}