Q1
How many equal sides does an isosceles triangle have?
ATwo
BThree
COne
DZero
ICSEClass 9 (ICSE)MathematicsCh 10 · Topic 1
Isosceles Triangles
An isosceles triangle has two equal sides, and the angles opposite these equal sides are also equal, a key geometric property.
Core concept
In an isosceles triangle, the two equal sides are called legs, and the angle between them is called the vertex angle.
How it works
The base angles (opposite the equal sides) are always equal, a fundamental theorem in isosceles triangle geometry.
Why it matters
The converse is also true - if two angles of a triangle are equal, then the sides opposite those angles are also equal.
Key detail
Understanding isosceles triangle properties helps solve geometry problems involving symmetry and angle calculations.
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Quick notes
• An isosceles triangle has two equal sides.
• These are called legs.
• The angle between legs is the vertex angle.
• Base angles (opposite equal sides) are equal.
• This is a fundamental isosceles triangle theorem.
• The converse is also true.
• Equal angles mean equal opposite sides.
• These properties help solve geometry problems.