8.
ΔDEF is an isosceles triangle, therefore:
[tex]\begin{gathered} m\angle DEF=m\angle DEG+m\angle FEG \\ \text{where:} \\ m\angle DEG=3y+4 \\ m\angle FEG=5y-10 \\ m\angle DEG=m\angle FEG \\ 3y+4=5y-10 \\ \text{solving for y:} \\ 2y=14 \\ y=7 \\ m\angle DEG=m\angle FEG=3(7)+4=25 \\ m\angle DEF=25+25 \\ m\angle DEF=50 \end{gathered}[/tex]
9.
C. Perpendicular bisector
A. Angle bisector
D. Altitude ( If your teacher mean height)
B. Median
10.
A. Circumcenter
B. Incenter
C. Orthocenter
D. Centroid
