Chapter 3.6, Problem 4PSA

To determine

The given triangle is an acute angle triangle

Explanation of Solution

Given information:

Given triangle ABC with marked figure

Formula used:

Vertical angles are always equal

Acute angle has all of its angles acute

Proof:

Since in a given triangle ABC,

  $\angle \text{DCE=}\angle \text{ACB=60}°$ , because they are vertical angles.

Now, triangle ABC has all of its angles acute measuring as $\text{60}°,50°\text{ and 70}°$

Hence, given triangle is acute angle triangle