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Mathematics

In the figure of question 14, if E is the mid point of median AD, then prove that :

Area (△ ABE) = 14\dfrac{1}{4} Area (△ ABC).

Theorems on Area

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Answer

We know that,

Median of a triangle divides it into two triangles of equal area.

In the figure of question 14, if E is the mid point of median AD, then prove that : Area Theorems, Concise Mathematics Solutions ICSE Class 9.

From figure,

AD is the median of Δ ABC, so it will divide Δ ABC into two equal triangles.

∴ Area of Δ ABD = Area of Δ ADC = 12\dfrac{1}{2} Area of Δ ABC

⇒ Area of Δ ABD = 12\dfrac{1}{2} Area of Δ ABC ………(1)

In Δ ABD,

Since, E is mid-point of AD,

∴ BE is the median.

∴ BE will divide Δ ABD into two equal triangles.

∴ Area of Δ ABE = Area of Δ BED = 12\dfrac{1}{2} Area of Δ ABD

⇒ Area of Δ ABE = 12\dfrac{1}{2} Area of Δ ABD ………(2)

Substituting value of Area of Δ ABD from equation (1) in (2), we get :

⇒ Area of Δ ABE = 12×12\dfrac{1}{2} \times \dfrac{1}{2} Area of Δ ABC

⇒ Area of Δ ABE = 14\dfrac{1}{4} Area of Δ ABC.

Hence, proved that area of Δ ABE = 14\dfrac{1}{4} area of Δ ABC.

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