Classifying Angles - SmartMathz - Free Printable

To classify each angle, we look at how wide the opening is between the two lines:

- Acute angle: Less than 90° — looks like a sharp “V” or small corner.
- Right angle: Exactly 90° — looks like the corner of a square or book (often marked with a little square).
- Obtuse angle: More than 90° but less than 180° — looks like a wide open mouth or lazy L.
- Straight angle: Exactly 180° — looks like a straight line.

Now let’s go row by row, left to right:

Row 1:
1. First angle: Wide opening — more than 90° → obtuse
2. Second angle: Very narrow — less than 90° → acute
3. Third angle: Narrow V shape — less than 90° → acute

Row 2:
4. Fourth angle: Perfect corner with square mark → right
5. Fifth angle: Wide opening — more than 90° → obtuse
6. Sixth angle: Also wide — more than 90° → obtuse

Row 3:
7. Seventh angle: Sharp V — less than 90° → acute
8. Eighth angle: Just one vertical line? Wait — actually, this is likely meant to be a straight angle if it's drawn as a single line segment with no bend. But looking closely, it’s just a vertical line — that doesn’t form an angle unless there are two rays. However, in context of worksheet design, this might be intended as a straight angle (180°) if it’s implying a flat line. But wait — re-examining: it’s drawn as a single vertical line segment. That’s not an angle. Hmm. Actually, in many worksheets, if they draw a single line, sometimes they mean “straight angle” — but technically you need two rays. Let me check the original image again mentally... Oh! In the third row, second column — it’s drawn as a single vertical line. But angles require two sides. This must be a trick or error? No — wait, perhaps it’s meant to represent a straight angle lying vertically? Unlikely. Alternatively, maybe it’s a typo and should have been horizontal? But in standard classification, if it’s just one line, it’s not an angle. However, given the pattern and common worksheet conventions, I think this is intended to be a straight angle — because all other boxes have two-line figures except this one. Actually, looking back at user’s image description: “third row, second column: | ” — that’s a single vertical line. But in geometry, an angle needs two rays from a vertex. So this might be misdrawn. BUT — in some curricula, they show a straight line and call it a straight angle even if drawn vertically. To match typical Grade 3 expectations, and since the instruction says “write straight, right, obtuse or acute”, and “straight” is an option, this is almost certainly meant to be straight. We’ll go with that.

Wait — correction: Upon double-checking standard interpretation — if only one line is shown, it cannot form an angle. But in this worksheet, every box has either two lines forming an angle OR one line for straight. The eighth figure is a single vertical line — which implies a 180° angle along that line. So yes, straight.

9. Ninth angle: Looks like a tilted L — wider than 90°? Let’s see: it opens up broadly — definitely more than 90° → obtuse

Actually, wait — ninth angle: drawn as two lines meeting at a point, opening to the left-down direction. It looks like about 100–120 degrees — so obtuse

Row 4:
10. Tenth angle: Single diagonal line — same issue as #8? Again, only one line. Must be intended as straight angle (180°), even though drawn diagonally. Yes — in worksheets, any single line segment without a bend is considered representing a straight angle.

But hold on — tenth figure: “\ ” — that’s a single slanted line. Same logic — straight

11. Eleventh angle: Small triangle-like shape — very narrow opening → acute

12. Twelfth angle: Wide opening, almost flat but bent — clearly more than 90° → obtuse

Let me list them in order grid-wise (row-major):

Grid positions:

Row 1: [1] obtuse, [2] acute, [3] acute
Row 2: [4] right, [5] obtuse, [6] obtuse
Row 3: [7] acute, [8] straight, [9] obtuse
Row 4: [10] straight, [11] acute, [12] obtuse

Wait — let me verify #9 again. Figure in row 3, column 3: drawn as two lines going down-right and down-left from top vertex — forms a wide angle — yes, >90° → obtuse. Correct.

#10: single diagonal line — straight angle → correct.

#11: small acute angle — yes.

#12: large obtuse — yes.

Final Answer:

obtuse
acute
acute
right
obtuse
obtuse
acute
straight
obtuse
straight
acute
obtuse