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Answer:
DE = 6 cm
Step-by-step explanation:
Let DE = x cm.
Since DE is parallel to AB therefore by the alternate interior angles theorem, m∠BAD = m∠ADE and m∠ABE = m∠DEB ............(1)
As AD is an angle bisector of ∠A, therefore m∠EAD = m∠DAB ; Since BE is an angle bisector of ∠B ⇒ m∠ABE = m∠EBD.
Therefore, from (1) We get , m∠EAD = m∠ADE and m∠EBD = m∠BED.
So, the triangles ADE and EDB are then isosceles with AE = ED and ED = DB.
So AE = DE = DB = x, and since the perimeter of ABDE is 30 cm, then
12 + x + x + x = 30
⇒ 12 + 3x = 30
⇒ x = 6
Hence, the length of DE is 6 cm.
In the given figure we can determine the coordinate of point M from the graph, we get:
We can also determine the coordinates of point N as:
Now, to determine the length of segment MN, we need to subtract the x-coordinate of M from the coordinates of N, we get:
Subtracting the fractions we get:
Now, to obtain the length of AB we need to subtract the x-coordinate of A from the x-coordinate of B.
The coordinates of A are determined from the graph:
The coordinates of B are:
Therefore, the length of segment AB is:
Now we do the same procedure to determine the segment of CD. The coordinates of C are:
The coordinates of D are:
Therefore, CD is:
Now, we determine MN as half the sum of the bases. The bases are AB and CD, therefore:
Therefore, we have proven that the median of a trapezoid equals half the sum of its bases.