Answer:
√[ (a + b)^2 + c^2 ].
Step-by-step explanation:
They are both equal in length because we have an isosceles trapezoid here. We see form the drawing it is symmetrical about the y axis.
The diagonal = the line joining points (b, c) and (-a, 0)
= √[ (b - -a)^2 + (c - 0)^2 ]
= √[ (a + b)^2 + c^2].
