|a1|+|a2|+|a3|+…+|an|
=2+4+6+…+2n-14n
=2(1+2+3…+n)-14n
=(n+1)(n+2)-14n
=n^2-11n+2
求两直线交点,解方程组
ax-2y=2a-4
2x+a^2y=2a^2+4
得x=2,y=2且a不等于三次根号-4
四边形面积为4