Question 1118688
WHICH SIDE?



There are two choices.


The two equal legs are each 13 feet, and the triangle's area is {{{(1/2)*13*13=169/2}}}


OR


The long side, hypotenuse, is 13 feet, making each congruent leg {{{13*sqrt(2)/2}}}; and then the triangle's area is {{{(1/2)(13sqrt(2)/2)(13sqrt(2)/2)=highlight_green(169/4)}}}.
If your description intends to mean, one and only one side is 13 feet, then this one is the area you want.