If `x` is real and `Delta(x)=|[x^2+x, 2x-1, x+3] , [3x+1, 2+x^2, x^2-3] , [x-3, x^2+4, 2x]|= a_0x^7+a_1x^6+a_2x^5+...+a_6x+a_7` then