4th Grade Geometry - Free Printable

Let’s solve this step by step.

We are given three triangles, and we’re told to:
1. Measure each angle in the triangle using a protractor (but since we can’t physically measure here, we’ll use geometry rules).
2. Add up the angles in each triangle.
3. Write the total in the middle of the triangle.
4. Notice what happens — you should notice that the sum of the interior angles of any triangle is always 180°.

But wait — let’s check each triangle carefully based on their shapes and markings.

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Triangle 1:
- It has a right angle symbol (a small square) → that means one angle is 90°.
- The other two angles look like they might be equal? Let’s see: it looks like an isosceles right triangle? Actually, no — looking at the shape, the two non-right angles appear different. But actually, if you look closely, the side opposite the top-left angle is longer than the side opposite the bottom-right angle — so they’re not equal.

Wait — but we don’t have actual measurements. However, in real life, when you measure with a protractor, you’d get numbers. Since this is a worksheet designed for learning, and all triangles must add to 180°, we can reason:

Actually — let’s think differently. Maybe these are drawn to scale? Or maybe we’re supposed to know that regardless of shape, the sum is always 180°.

But the instruction says: “Use a protractor to measure...” — which implies we should simulate measuring.

Since I can’t physically measure, I’ll assume standard values based on typical textbook diagrams.

Looking again:

Triangle 1: Right triangle. One angle = 90°. The other two — let’s estimate from drawing:
- Top-left angle: looks about 45°? Wait, no — the sides aren’t equal. The vertical leg is shorter than the horizontal leg? Actually, in the diagram, the vertical leg is on the right, and the hypotenuse goes from top-left to bottom-right. The angle at top-left seems smaller than the angle at bottom-right.

Actually, let me try to assign reasonable values based on common problems.

Alternatively — perhaps the key point is NOT the individual angles, but the SUM.

The question ends with: “What do you notice?” — which strongly suggests the answer is that all triangles’ angles add up to 180°.

So even without exact measurements, we can say:

For Triangle 1: Suppose angles are 90°, 60°, 30° → sum = 180°
Or 90°, 50°, 40° → still 180°

Triangle 2: Looks like an acute triangle, possibly equilateral? All angles look similar. If equilateral, each is 60° → 60+60+60=180°

Triangle 3: Obtuse triangle — one angle >90°. Say 120°, then the other two might be 30° and 30° → 180°

In every case, the sum is 180°.

So the main thing to notice is: No matter what kind of triangle it is — right, acute, obtuse — the three interior angles always add up to 180 degrees.

Therefore, for each triangle, after measuring (or calculating), you write 180 in the middle.

And what you notice: The sum of the angles in any triangle is always 180°.

This is a fundamental rule in geometry called the Triangle Angle Sum Theorem.

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Final Answer:
For each triangle, the sum of the interior angles is 180°. You will notice that no matter the type of triangle (right, acute, or obtuse), the total of its three angles always equals 180 degrees.