ABC and BDE are two equilateral triangles such that D is the mid-point of BC. Then, ar (ΔBDE) = ¼ ar (ΔABC).
True
Given, $\triangle A B C$ and $\triangle B D E$ are two equilateral triangles.
$\therefore$ Area of an equilateral $\triangle A B C=\frac{\sqrt{3}}{4} \times(\text { Side })^{2}=\frac{\sqrt{3}}{4}(B C)^{2}$ $\ldots(1)$
$[\because$ in equilateral $\triangle A B C, A B=B C=A C]$
Also, given $D$ is the mid-point of $B C$.
$\therefore$ $B D=D C=\frac{1}{2} B C$ ...(ii)
Now, area of an equilateral $\triangle B D E=\frac{\sqrt{3}}{4} \times(\text { Side })^{2}$
$=\frac{\sqrt{3}}{4} \times(B D)^{2}$ $[\because$ in equilateral $\triangle B D E, B D=D E=B E]$
$=\frac{\sqrt{3}}{4} \times\left(\frac{1}{2} B C\right)^{2}$ [from Eq. (ii)]
$=\frac{\sqrt{3}}{4} \times \frac{1}{4} B C^{2}=\frac{1}{4}\left(\frac{\sqrt{3}}{4} B C^{2}\right)$
$\therefore$ Area of $\triangle B D E=\frac{1}{4}$ Area of $\triangle A B C$