TRIANGLES (tri- means 3). • Triangles ALWAYS have 3 sides. • The interior angles of a triangle add up to 180 degrees. • There are following types of triangles: – Equilateral Triangle – Isosceles Triangle – Right- Angled Triangle – Scalene Triangle We will learn about Equilateral Triangle.
Equilateral Triangle • An equilateral triangle has got 3 sides of equal length and 3 angles that are equal. • Since ALL the angles in a triangle add up to 180º then 180 divided by 3 must be 60º.
EQUILATERAL TRIANGLE
• Construction • Properties
STEP 1
Draw a straight line AB of 5cm. A
5cm
B
STEP 2
A
5cm
B
Open the compass for 5cm and make an arc from B.
STEP 3 C
A
5cm
B
Intersect the arc with the same compass at point C from A.
STEP 4 C
A
5cm
B
Join the intersection point with both of ends.
STEP 5 The Equilateral Triangle ABC is ready. Here-
C 60° m
5c m
5c
Sides AB=BC=AC=5cm &
60° A
60° 5cm
B
Angles ∠ABC= ∠BCA= ∠ CAB=60°
Properties of Equilateral Triangle • All side are equal. • Angles of every equilateral triangle are equal to 60°. • Every altitude is also a median and bisector. • Every median is also an altitude and bisector. • Every bisector is also an altitude and median. BACK NEXT
• References – Text Book – www.icteachers.co.uk.
• Subject Teacher – Mrs. Jatinder Kaur
• Prepared By – Gagandeep Kaur (9TH ) – Harsimran Kaur (9TH )
• Edited By – Computer Staff END