Answer:
bd = 120 units
Step-by-step explanation:
The diagonals of a parallelogram bisect each other. This means ...
be = de
x^2 -40 = 6x . . . . . . substitute given expressions
x^2 -6x -40 = 0 . . . . subtract 6x
(x -10)(x +4) = 0 . . . . . factor
Solutions are the values of x that make the factors zero. These are -4 and +10. Only the positive value is of interest here, since the segment lengths must be positive.
de = 6x = 6(10) = 60
The length of bd is twice this length, so ...
bd = 120 units
