m∠CDF + m∠EDF = ∠CDE
[tex]x + 25° + 65° = 3x + 10[/tex]
[tex]x + 90° = 3x + 10[/tex]
[tex]90° = 3x + 10 - x[/tex]
[tex]90° = 2x + 10[/tex]
[tex]2x + 10 = 90[/tex]
[tex]2x = 90 - 10[/tex]
[tex]2x = 80[/tex]
[tex]x = \frac{80}{2} [/tex]
[tex]x = 40°[/tex]
m∠CDE
= 3 × 40 + 10
= 120 + 10
= 130°
Then , m∠CDF =
[tex]x + 25 \\ = 40 + 25 \\ = 65°[/tex]
•°• m∠CDF = 65°
