X-12 will give the other number
The required proof of parallelogram is given below,
What is parallelogram?
A parallelogram is a straightforward quadrilateral with two sets of parallel sides in Euclidean geometry. The opposing or confronting sides and the opposing angles in a parallelogram are of equal length.
For a parallelogram, opposite sides are always equal and parallel.
So for the given parallelogram, we get AD = BC and AD and BC are parallel.
AD and BC is parallel and DC is common side, therefore,
......(1)
Given
.......(2)
Therefore, from condition (1) and (2), we get

If
then DC bisects the angle
. [Proved]
To learn more about parallelogram from the given link
brainly.com/question/970600
#SPJ1
Since angles A and C are equivalent, then angles B and D must also be equivalent. So if
angle B = angle D then...
7x + 15 = 8x
Now we just solve for x
7x + 15 = 8x
15 = 8x - 7x
15 = x
We Can check to see if it is correct by substituting 15 in for x in the equation..
7x + 15 = 8x
7 (15)+15 = 8 (15)
105 +15 = 120
120 = 120
It checks! angles B and D = 120 degrees
If the slopes of the 2 lines are equal then they are parallel.
If m1m2 = -1 (where m1 and m2 are the slopes of the 2 lines) then they are perpendicular.
If the 2 slopes do not match either the first or second conditions then they are neither parallel or perpendicular.