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diff --git a/src/math/big/example_test.go b/src/math/big/example_test.go
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+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package big_test
+
+import (
+	"fmt"
+	"log"
+	"math"
+	"math/big"
+)
+
+func ExampleRat_SetString() {
+	r := new(big.Rat)
+	r.SetString("355/113")
+	fmt.Println(r.FloatString(3))
+	// Output: 3.142
+}
+
+func ExampleInt_SetString() {
+	i := new(big.Int)
+	i.SetString("644", 8) // octal
+	fmt.Println(i)
+	// Output: 420
+}
+
+func ExampleFloat_SetString() {
+	f := new(big.Float)
+	f.SetString("3.14159")
+	fmt.Println(f)
+	// Output: 3.14159
+}
+
+func ExampleRat_Scan() {
+	// The Scan function is rarely used directly;
+	// the fmt package recognizes it as an implementation of fmt.Scanner.
+	r := new(big.Rat)
+	_, err := fmt.Sscan("1.5000", r)
+	if err != nil {
+		log.Println("error scanning value:", err)
+	} else {
+		fmt.Println(r)
+	}
+	// Output: 3/2
+}
+
+func ExampleInt_Scan() {
+	// The Scan function is rarely used directly;
+	// the fmt package recognizes it as an implementation of fmt.Scanner.
+	i := new(big.Int)
+	_, err := fmt.Sscan("18446744073709551617", i)
+	if err != nil {
+		log.Println("error scanning value:", err)
+	} else {
+		fmt.Println(i)
+	}
+	// Output: 18446744073709551617
+}
+
+func ExampleFloat_Scan() {
+	// The Scan function is rarely used directly;
+	// the fmt package recognizes it as an implementation of fmt.Scanner.
+	f := new(big.Float)
+	_, err := fmt.Sscan("1.19282e99", f)
+	if err != nil {
+		log.Println("error scanning value:", err)
+	} else {
+		fmt.Println(f)
+	}
+	// Output: 1.19282e+99
+}
+
+// This example demonstrates how to use big.Int to compute the smallest
+// Fibonacci number with 100 decimal digits and to test whether it is prime.
+func Example_fibonacci() {
+	// Initialize two big ints with the first two numbers in the sequence.
+	a := big.NewInt(0)
+	b := big.NewInt(1)
+
+	// Initialize limit as 10^99, the smallest integer with 100 digits.
+	var limit big.Int
+	limit.Exp(big.NewInt(10), big.NewInt(99), nil)
+
+	// Loop while a is smaller than 1e100.
+	for a.Cmp(&limit) < 0 {
+		// Compute the next Fibonacci number, storing it in a.
+		a.Add(a, b)
+		// Swap a and b so that b is the next number in the sequence.
+		a, b = b, a
+	}
+	fmt.Println(a) // 100-digit Fibonacci number
+
+	// Test a for primality.
+	// (ProbablyPrimes' argument sets the number of Miller-Rabin
+	// rounds to be performed. 20 is a good value.)
+	fmt.Println(a.ProbablyPrime(20))
+
+	// Output:
+	// 1344719667586153181419716641724567886890850696275767987106294472017884974410332069524504824747437757
+	// false
+}
+
+// This example shows how to use big.Float to compute the square root of 2 with
+// a precision of 200 bits, and how to print the result as a decimal number.
+func Example_sqrt2() {
+	// We'll do computations with 200 bits of precision in the mantissa.
+	const prec = 200
+
+	// Compute the square root of 2 using Newton's Method. We start with
+	// an initial estimate for sqrt(2), and then iterate:
+	//     x_{n+1} = 1/2 * ( x_n + (2.0 / x_n) )
+
+	// Since Newton's Method doubles the number of correct digits at each
+	// iteration, we need at least log_2(prec) steps.
+	steps := int(math.Log2(prec))
+
+	// Initialize values we need for the computation.
+	two := new(big.Float).SetPrec(prec).SetInt64(2)
+	half := new(big.Float).SetPrec(prec).SetFloat64(0.5)
+
+	// Use 1 as the initial estimate.
+	x := new(big.Float).SetPrec(prec).SetInt64(1)
+
+	// We use t as a temporary variable. There's no need to set its precision
+	// since big.Float values with unset (== 0) precision automatically assume
+	// the largest precision of the arguments when used as the result (receiver)
+	// of a big.Float operation.
+	t := new(big.Float)
+
+	// Iterate.
+	for i := 0; i <= steps; i++ {
+		t.Quo(two, x)  // t = 2.0 / x_n
+		t.Add(x, t)    // t = x_n + (2.0 / x_n)
+		x.Mul(half, t) // x_{n+1} = 0.5 * t
+	}
+
+	// We can use the usual fmt.Printf verbs since big.Float implements fmt.Formatter
+	fmt.Printf("sqrt(2) = %.50f\n", x)
+
+	// Print the error between 2 and x*x.
+	t.Mul(x, x) // t = x*x
+	fmt.Printf("error = %e\n", t.Sub(two, t))
+
+	// Output:
+	// sqrt(2) = 1.41421356237309504880168872420969807856967187537695
+	// error = 0.000000e+00
+}