Mrs.D Math · 8th Grade

MIRROR
MATCH

Angle-Angle Similarity · Similar Triangles
📐 Angles
📏 Side Lengths
❔ Similar
⚖️ Proportional
📐 ∠A ≅ ∠D
📏 6⁄3 = 8⁄4
🔍 Similar? Prove it!
📺 Mrs.D Math Lesson
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📚 Similar Triangles

What Makes Triangles Similar?

Similar triangles have the same shape but can be different sizes. There are two ways to prove it:

1
Equal Angles (AA): If two angles of one triangle are congruent to two angles of another, the triangles are similar.
∠A = 50°, ∠B = 60° and ∠D = 50°, ∠E = 60° → similar!
2
Proportional Sides: Divide each pair of corresponding sides. If every ratio is the same, the triangles are similar.
6⁄3 = 8⁄4 = 10⁄5 = 2 → similar!

Solving for a Missing Angle or Side

✓
Missing angle: The three angles of a triangle always add up to 180°.
50° + 60° + ? = 180° → ? = 70°
✓
Corresponding angles: In similar triangles, matching angles are equal.
✓
Missing side: Set up a proportion with corresponding sides, then solve.
x⁄6 = 8⁄4 → x = 12

How to Play

🔍
Similar or Not? — Study the two triangles and decide if they are similar — and why!
🧩
Solve for Missing — The triangles ARE similar. Find the missing angle or side length.
🆕
Mixed — Both types together for the ultimate challenge!
🧮
Calculator: Tap the gold calculator button in the corner any time you need it!
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SIMILAR OR NOT?
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