Drao a vertical line from to E and another from B to F.
\[ED=CF=x\]
and \[8 +2x=12\]
since \[AB=EF\]
. Hence \[x=2\]
.Now draw the right angled triangle DBF.
Then
\[DF= \sqrt{DF^2 +FB^2} =\sqrt{10^2+9^2} =13.45 cm\]
Length of the Diagonal of an Isosceles Trapezium
An isosceles trapezium has one line of symmetry. We can use this to find the length of the diagonal.
Now draw the right angled triangle DBF.
Now draw the right angled triangle DBF.