Libgdx Drawing a triangle cannot resolve method “render ”

I am looking to draw a triangle. I found a lot of code such as : https://github.com/libgdx/libgdx/wiki/My-First-Triangle-%28Example%29

The code I found are old I think; if I use

mesh.render(GL20.GL_TRIANGLES, 0, 3);

Compiler cannot resolve method

How can I draw a triangle or solve this problem?