In triangle DEF, the angle E is 5 times and the angle F is 4 times the angle D. Find all the corners of the triangle DEF.

1. Suppose the angle D of this triangle DEF is x degrees.

2. Determine the angle E.

x * 5 = 5x degrees.

3. Let’s calculate the value of the angle F.

x * 4 = 4x degrees.

4. Let’s compose an equation with the help of which we find the angle D.

x + 5x + 4x = 180;

10x = 180;

x = 180/10 = 18 °.

Answer: Angle D is x = 18 °, E = x * 5 = 18 * 5 = 90 °, F = x * 4 = 18 * 4 = 72 °.