(a+b+c)^3=a^3+b^3+c^3+3a^2b+3ab^2+3a^2c+3ac^2+3b^2c+3bc^2+6abc

The second method is to expand the application of Yang Hui Triangle.

Take (a+b) as a whole to get (a+b)+c 3, and you can get a (a+b) 3, so you can calculate the direct use of Yang Hui triangle.