Answer: The length of BC is 7
Step-by-step explanation: Assuming the lengths of the opposite sides of the quadrilateral are congruent, then
AB=DC and
AD=BC
Inputting the values of AB, DC and AD as given in the question:
x + 8 = 3x ...(1)
x + 3=? ...(2)
We have to solve for the value of x to get the actual lengths and thus ascertain BD.
From equation (1):
8 = 3x - x
8 = 2x
8/2 = x
Therefore, x = 4.
If x = 4 then equation(2) would be
4 + 3= 7.
Hence, the actual lengths of the quadrilateral are:
AB = 4 + 8. DC = 3(4)
=12. =12.
AD = 4 + 3. AD = BC
= 7. Therefore, BC = 7.
Hence, it is confirmed that quadrilateral ABCD is a parallelogram since both the opposite sides are proven to be congruent.