prove that `[ [a-b-c , 2a , 2a ] , [2b , b-c-a , 2b ] ,[2c ,2c,c-a-b]]`= `(a+b+c)^3`

Explanation

To prove that the determinant of the matrix

\[
\begin{vmatrix}
a-b-c & 2a & 2a \\
2b & b-c-a & 2b \\
2c & 2c & c-a-b
\end{vmatrix}
...