math: Add a function example

When I browsed the source code, I saw that there is no corresponding example of this function. I am not sure if there is a need for an increase, this is my first time to submit CL.

Change-Id: Idbf4e1e1ed2995176a76959d561e152263a2fd26
Reviewed-on: https://go-review.googlesource.com/c/go/+/230741
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

1 files changed, 8 insertions, 0 deletions

diff --git a/src/math/example_test.go b/src/math/example_test.go
index 50c7426979..ce9c383256 100644
--- a/src/math/example_test.go
+++ b/src/math/example_test.go
@@ -219,3 +219,11 @@ func ExampleTrunc() {
 	// 3.00
 	// -1.00
 }
+
+func ExampleCbrt() {
+	fmt.Printf("%.2f\n", math.Cbrt(8))
+	fmt.Printf("%.2f\n", math.Cbrt(27))
+	// Output:
+	// 2.00
+	// 3.00
+}