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Gyaan Maths
CBSE · Class 6-12
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Class 7 · Ganita Prakash
Unit 7 · Class 7Ganita Prakash
A Tale of Three Intersecting Lines
Triangles: properties, angle sum, exterior angle.
Lessons
3 concepts
1
Angle Sum Property
All three interior angles add to
180
°
180°
180°
. In an equilateral, each is
60
°
60°
60°
.
2
Exterior Angle
Exterior angle at a vertex = sum of the two interior angles at the other two vertices.
3
Triangle Inequality
For any triangle with sides
a
,
b
,
c
a, b, c
a
,
b
,
c
:
a
+
b
>
c
a+b>c
a
+
b
>
c
,
b
+
c
>
a
b+c>a
b
+
c
>
a
,
a
+
c
>
b
a+c>b
a
+
c
>
b
. Reverse: cannot form triangle if any fails.
Skills to practise
Skill · medium
A Tale of Three Intersecting Lines — Practice