Given: <DFE = <CDF, CF || DE, FG=2x, DG=18

Prove: x=9

FG = DG
CDEF is a parallelogram
Given
CD || FE
The diagonals of a parallelogram bisect each other
x=9
Definition
Substitution
Equal alternate interior angles mean parallel lines
Algebra
2x=18
CE bisects DF at G
Definition
<DFE = <CDF, CF || DE, FG=2x, DG=18