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Area of Plane Figures

  • Area of a triangle:
    • Area of a triangle =
    • All the congruent triangles are equal in area, but the triangles having equal areas may or may not be congruent.


Example: ΔABC is isosceles with AC = BC = 6 cm. AE and BD are the medians and AF = 4 cm. What is the area of ΔABD?



Solution: In ΔABE and ΔBAD, we have

BE = AD                      ]

∠ABE = ∠BAD          [Angles opposite to equal sides]

AB = AB                      [Common]

⇒ ΔABE ΔBAD       [By SAS congruency criterion]

Area (ΔABE) = Area (ΔBAD)

Now, Area ΔABE =

⇒ Area ΔABD = 6 cm2

  • Area of triangle using Heron's formula:

When all the three sides of a triangle are given, its area can be calcula…

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