Answer:
13√2
Explanation:
The areas of the larger triangle, and the smaller triangle (formed when the larger triangle was cut by the parallel line) are similar. Therefore we can compare their areas:
Area1/Area2 = (Length1)^2/(Length2)^2,
x/2x = (Length1)^2/(26)^2,
1/2 = (Length1)^2/676,
(Length1)^2 = 676/2 = 338
Length1 = √1352 = 13√2