class Array def mul(x) m = self.size - 1 n = x.size - 1 c = Array.new(m + 1) c.each_index {|i| c[i] = Array.new(m + 1, 0)} for i in 0..m for j in 0..m for k in 0..n c[i][j] += self[i][k] * x[k][j] end end end c end end a = [[-1, -1, 2], [-…