- AScalene
- BIsosceles
- CEquilateral
- DObtuse
Step-by-Step Solution
Every equilateral triangle has all angles equal to 60°, so by AA criterion all equilateral triangles are similar.
Answer: C) Equilateral
All ____ triangles are similar to one another regardless of their size.
Class 10Triangles (Similarity)Geometry — Similarity
Key idea: Similarity vs congruence
**Congruent**: same shape AND same size. All corresponding parts equal.
**Similar**: same shape, possibly DIFFERENT size. Corresponding angles equal; corresponding sides PROPORTIONAL (in fixed ratio k).
If two triangles are similar with scale factor :
- Corresponding sides differ by factor .
- Corresponding angles are equal (always, by definition).
- Areas differ by factor — critical fact, and a common test question.
**Examples**:
- Equilateral triangles are ALL similar (same angles 60°-60°-60°).
- A photograph and its enlarged print are similar.
- Two right triangles sharing one acute angle are similar (AA).
**Similar**: same shape, possibly DIFFERENT size. Corresponding angles equal; corresponding sides PROPORTIONAL (in fixed ratio k).
If two triangles are similar with scale factor :
- Corresponding sides differ by factor .
- Corresponding angles are equal (always, by definition).
- Areas differ by factor — critical fact, and a common test question.
**Examples**:
- Equilateral triangles are ALL similar (same angles 60°-60°-60°).
- A photograph and its enlarged print are similar.
- Two right triangles sharing one acute angle are similar (AA).
Master this chapter in 30 minutes a day.
Don't just memorise the answer — build a daily practice habit.
Practice 5 Similar Questions Free →All Triangles (Similarity) practice questions
More Class 10 Triangles (Similarity) practice
Two similar triangles have corresponding sides in ratio 3 : 5. The ratio of their…In ΔABC, DE ∥ BC with D on AB and E on AC. If AD = 2 cm, DB = 3 cm and AC = 10 cm, find…ΔABC ~ ΔDEF with a scale factor (AB : DE) of 3 : 4. If the area of ΔABC is 45 cm², find…The square of the hypotenuse of a right triangle equals the sum of the squares of the…A right triangle has legs 3 cm and 4 cm. Find the length of its hypotenuse in cm.