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Similar Triangles Calculator

Check whether two triangles are similar or find the missing length of a triangle with the help of this similar triangles calculator.

△ABC

millimeters (mm)

centimeters (cm)

meters (m)

kilometers (km)

inches (in)

feets (ft)

yards (yd)

miles (mi)

degrees (deg)

radians (rad)

millimeters (mm)

centimeters (cm)

meters (m)

kilometers (km)

inches (in)

feets (ft)

yards (yd)

miles (mi)

degrees (deg)

radians (rad)

millimeters (mm)

centimeters (cm)

meters (m)

kilometers (km)

inches (in)

feets (ft)

yards (yd)

miles (mi)

degrees (deg)

radians (rad)

millimeters (mm)

centimeters (cm)

meters (m)

kilometers (km)

inches (in)

feets (ft)

yards (yd)

miles (mi)

△DEF

millimeters (mm)

centimeters (cm)

meters (m)

kilometers (km)

inches (in)

feets (ft)

yards (yd)

miles (mi)

degrees (deg)

radians (rad)

millimeters (mm)

centimeters (cm)

meters (m)

kilometers (km)

inches (in)

feets (ft)

yards (yd)

miles (mi)

degrees (deg)

radians (rad)

millimeters (mm)

centimeters (cm)

meters (m)

kilometers (km)

inches (in)

feets (ft)

yards (yd)

miles (mi)

degrees (deg)

radians (rad)

millimeters (mm)

centimeters (cm)

meters (m)

kilometers (km)

inches (in)

feets (ft)

yards (yd)

miles (mi)

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Similar Triangles Calculator

Our similar triangles calculator lets you quickly check if two triangles are similar and compute any missing side lengths based on proportionality.

What Are Similar Triangles?

Similar triangles are triangles with identical shapes but not necessarily the same size. They maintain the same angles and have sides in proportion. Unlike congruent triangles, which match in both shape and size, similar triangles are indicated with the symbol ‘~’.

Formulas for Similar Triangles

For triangles △ABC and △DEF, similarity (△ABC ~ △DEF) requires:

  • ∠A = ∠D, ∠B = ∠E, ∠C = ∠F
  • AB / DE = BC / EF = AC / DF

Similar vs. Congruent Triangles

Similar Triangles Congruent Triangles
Same shape but different size Same shape and same size
Symbol: ‘~’ Symbol: ‘≅’
Corresponding sides proportional Corresponding sides equal

Key Theorems to Prove Similarity

Even without full knowledge of all sides and angles, these theorems help establish similarity:

1. AA (Angle-Angle)

If two angles of one triangle are equal to two angles of another, the triangles are similar.

2. SAS (Side-Angle-Side)

If two sides are proportional and the included angle is equal, the triangles are similar.

3. SSS (Side-Side-Side)

If all three corresponding sides are proportional, the triangles are similar.

Steps to Check Triangle Similarity

  • List all known sides and angles of the triangles.
  • Apply AA, SAS, or SSS to test for similarity.
  • If conditions are met, denote similarity using ‘~’.

Example

Check if △XYZ and △LMN are similar:

  • ∠X = 50°, ∠Y = 60°
  • ∠L = 60°, ∠N = 50°

Calculating the third angles:

  • ∠Z = 180° - (50° + 60°) = 70°
  • ∠M = 180° - (60° + 70°) = 50°

Since two pairs of angles are equal, △XYZ ~ △LMN by the AA theorem.

Finding Missing Sides

  • Determine the scale factor by dividing corresponding known sides.
  • Multiply or divide other sides by the scale factor to find missing lengths.
  • Apply proportionality for all remaining sides as needed.

How the Calculator Works

Enter known sides or angles, and the calculator can confirm similarity and solve for missing side lengths.

Inputs for Similarity Check

  • Select the criterion (AA, SAS, or SSS)
  • Input available sides or angles of the triangles

Output: Confirmation of similarity.

Inputs for Missing Sides

  • Input known sides for both triangles
  • Compute the scale factor

Output: Missing sides, areas, and perimeters of triangles.

Applications

  • Students and teachers can verify and explain geometric problems.
  • Architects, designers, and engineers can scale objects accurately.

FAQs

Are Similar Triangles and Congruent Triangles the Same?

No. Similar triangles share the same shape but differ in size; congruent triangles match in both shape and size.

Are All Equilateral Triangles Similar?

Yes, all equilateral triangles are similar since all angles are equal.

How Do I Calculate Side Ratios?

For similar triangles with sides X, Y, Z and x, y, z: X:x = Y:y = Z:z

Properties of Similar Triangles

  • Same shape, different size
  • Equal corresponding angles
  • Proportional corresponding sides

How to Identify Similar Right Triangles?

Right triangles with proportional corresponding sides are similar. Use the right triangle similarity calculator for accuracy.

References

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