S=c*h/2 ⇒h =2*120/26 =120/13 =9 7/13 < 26/2=13 .<br>
h² =x(26-x)
x² -26x +(120/13)² =0 ;
x=13 +√(169+)...>26
D =13² -(120/13)² =(13 -120/13)(13+120/13)=49/13*289/13=(7*17/13)² ;
√D =7*17/13;
x₁ =13 - 7*17/ 13=50/13;
x₂ =13 +7*17/13 > 13 = 26/2
a =√(120/13² + (50/13)²) =10/13*√(12² +5)² =10/13*13 =10