The sum has n terms: k=1∑n(x+2k−2)(x+2k).
Expanding and summing gives nx2+2n2x+34n(n2−1)=38n.
Dividing by n and simplifying: 3x2+6nx+4n2−12=0.
Discriminant =36n2−12(4n2−12)=12(12−n2).
Difference of roots =323(12−n2).
For two consecutive even integers, this difference =2.
36−3n2=3⇒n2=9⇒n=3.
For n=3: x=3−9±3=−2 or −4, which are consecutive even integers.