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If one vertex of an equilateral triangle of side $'a'$ lies at the origin and the other lies on the line $x - \sqrt{3} y = 0$ then the co-ordinates of the third vertex are :
$(0, a)$
$\left( {\frac{{\sqrt 3 \,a}}{2}\,\,,\,\, - \,\frac{a}{2}} \right)$
$(0, - a)$
all of the above
Solution
make a figure and interpret
Slope of the line $x=\sqrt{3} y$ is $\frac{1}{\sqrt{3}}$ which is $30^{\circ}$ with the positive $x$ -axis. As it is an equilateral triangle the other vertex must be on $x=-\sqrt{3} y$
Let the side be $(x, y)$. Hence, $x^{2}+y^{2}=a^{2}$
$4 y^{2}=a^{2}$
$y=\pm \frac{a}{2}$
similarily, $x=\pm \frac{\sqrt{3} a}{2}$
Hence, if the triangle lies in the 1 st quadrant and 4 th quadrant vertex is $\left(\frac{\sqrt{3} a}{2},-\frac{a}{2}\right)$
If the triangle lies in the 2 nd and 3 rd quadrant the vertex is $\left(-\frac{\sqrt{3} a}{2},-\frac{a}{2}\right)$