Answer:
Step-by-step explanation:
Because the trapezoid is isosceles, the two diagonals are congruent. This can be shown by ASA.
ACD = BDC Properties of parallel lines.
DC = DC A line is equal to itself
DBA = CAB Property of parallel lines.
AC = DB Parts of Congruent triangles are congruent
3x + 15 = 7x - 9 Add 9 to both sides
3x + 15 + 9 = 7x
3x + 24 = 7x Subtract 3x from both sides.
24 = 7x - 3x
24 = 4x Divide by 4
24/4 = 4x/4
x = 6
