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Find the missing angles in various polygons using the worksheet provided.

A worksheet titled "Finding Missing Angles in a Polygon" with eight numbered geometric figures, each showing some angles and one missing angle labeled as x°, requiring calculation to find the unknown angle.

A worksheet titled "Finding Missing Angles in a Polygon" with eight numbered geometric figures, each showing some angles and one missing angle labeled as x°, requiring calculation to find the unknown angle.

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Show Answer Key & Explanations Step-by-step solution for: Angles in Polygons Worksheets - Math Monks
Let's solve each problem step by step using geometric principles, such as the sum of interior angles in polygons and properties of parallel lines, triangles, and quadrilaterals.

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🔷 Problem 1: Quadrilateral



Given angles:
- 135°
- 60°
- 50°
- x°

Sum of interior angles in a quadrilateral = $ (4 - 2) \times 180^\circ = 360^\circ $

$$
135 + 60 + 50 + x = 360 \\
245 + x = 360 \\
x = 360 - 245 = 115^\circ
$$

Answer: $ x = 115^\circ $

---

🔷 Problem 2: Quadrilateral with two right angles



Angles:
- 90° (right angle)
- 90° (right angle)
- 50°
- x°

Sum = 360°

$$
90 + 90 + 50 + x = 360 \\
230 + x = 360 \\
x = 130^\circ
$$

Answer: $ x = 130^\circ $

---

🔷 Problem 3: Triangle with two equal sides (isosceles)



Marked with tick marks → two sides are equal → base angles are equal.

One angle is 60°, and one angle is $ x^\circ $. The triangle has two equal sides, so the angles opposite them are equal.

But only one angle is labeled: 60°. Let’s see which side it's on.

From the diagram:
- One angle is 60°
- Two sides are marked equal → the angles opposite those sides are equal.
- So if the 60° is at the bottom-left, and the two equal sides are from the top to bottom corners, then the two base angles are equal?

Wait — let's interpret:

The triangle has:
- A 60° angle at the bottom-left
- Two sides marked with ticks: one from the top vertex to bottom-left, and one from top to bottom-right → so the two sides from the top are equal → triangle is isosceles with apex at the top
→ So the two base angles (bottom-left and bottom-right) are equal.

But we are given:
- Bottom-left = 60°
- So bottom-right must also be 60°
- Then the top angle $ x $ is:

$$
x = 180 - 60 - 60 = 60^\circ
$$

So this is an equilateral triangle!

Answer: $ x = 60^\circ $

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🔷 Problem 4: Heptagon (7 sides)



Sum of interior angles in a polygon: $ (n - 2) \times 180^\circ $

For $ n = 7 $:
$ (7 - 2) \times 180 = 5 \times 180 = 900^\circ $

Given angles:
- 130°
- 122°
- 130°
- 130°
- 138°
- 128°
- $ x^\circ $

Add known angles:

$$
130 + 122 = 252 \\
252 + 130 = 382 \\
382 + 130 = 512 \\
512 + 138 = 650 \\
650 + 128 = 778
$$

So:

$$
778 + x = 900 \\
x = 900 - 778 = 122^\circ
$$

Answer: $ x = 122^\circ $

---

🔷 Problem 5: Pentagon (5 sides)



Sum of interior angles: $ (5 - 2) \times 180 = 3 \times 180 = 540^\circ $

Angles given:
- 120°
- 107°
- 90° (right angle)
- 90° (right angle)
- $ x^\circ $

Sum of known angles:

$$
120 + 107 = 227 \\
227 + 90 = 317 \\
317 + 90 = 407
$$

Then:

$$
407 + x = 540 \\
x = 540 - 407 = 133^\circ
$$

Answer: $ x = 133^\circ $

---

🔷 Problem 6: Quadrilateral



Angles:
- 50°
- 140°
- 70°
- $ x^\circ $

Sum = 360°

$$
50 + 140 + 70 + x = 360 \\
260 + x = 360 \\
x = 100^\circ
$$

Answer: $ x = 100^\circ $

---

🔷 Problem 7: Parallelogram-like shape (Quadrilateral)



Looks like a parallelogram or trapezoid. Angles given:
- Top-left: $ x^\circ $
- Top-right: 60°
- Bottom-left: 60°
- Bottom-right: 120°

Note: Opposite angles in a parallelogram are equal.

Check:
- Top-right = 60°, bottom-left = 60° → same → possible
- Bottom-right = 120° → so top-left should be 120°?

But wait: In a parallelogram, adjacent angles are supplementary (add to 180°)

Check:
- If top-right = 60°, then adjacent angle (bottom-right) should be 120° → matches
- Similarly, top-left = $ x $, adjacent bottom-left = 60° → so $ x + 60 = 180 $? No, unless it's a parallelogram.

Wait: Is this a parallelogram?

Look at angles:
- Top-left: $ x $
- Top-right: 60°
- Bottom-left: 60°
- Bottom-right: 120°

If it's a parallelogram:
- Opposite angles equal → top-left = bottom-right = 120°
- Top-right = bottom-left = 60° → matches

So yes! This is a parallelogram.

Thus:
- $ x = 120^\circ $

Alternatively, check sum:

$$
x + 60 + 60 + 120 = 360 \\
x + 240 = 360 \\
x = 120^\circ
$$

Answer: $ x = 120^\circ $

---

🔷 Problem 8: Rhombus (or kite-shaped quadrilateral)



Looks like a rhombus (all sides equal), but not necessarily.

Angles:
- Top: 140°
- Left: 40°
- Right: $ x^\circ $
- Bottom: 140°

Wait — notice symmetry.

Opposite angles in a rhombus are equal.

Top = 140°, bottom = 140° → OK

Left = 40°, so right should be 40°? But labeled as $ x $

Wait: But sum of angles:

$$
140 + 40 + x + 140 = 360 \\
320 + x = 360 \\
x = 40^\circ
$$

So $ x = 40^\circ $

But wait — is that consistent?

In a rhombus, opposite angles are equal → top and bottom both 140° → OK

Left and right: both should be equal → so $ x = 40^\circ $

Yes.

Also, adjacent angles are supplementary:

- 140° + 40° = 180° → yes

So all good.

Answer: $ x = 40^\circ $

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Final Answers:



| Problem | Answer |
|--------|--------|
| 1 | $ 115^\circ $ |
| 2 | $ 130^\circ $ |
| 3 | $ 60^\circ $ |
| 4 | $ 122^\circ $ |
| 5 | $ 133^\circ $ |
| 6 | $ 100^\circ $ |
| 7 | $ 120^\circ $ |
| 8 | $ 40^\circ $ |

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Parent Tip: Review the logic above to help your child master the concept of interior angles of a polygon worksheet.
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