MCQ
If three points $(0,0),(3, \sqrt{3})$ and $(3, \lambda)$ form an equilateral triangle, then $\lambda=$
  • A
    $-4$
  • None of these
  • C
    $-3$
  • D
    $2$

Answer

Correct option: B.
None of these
Explanation:
Let the points $(0,0),(3, \sqrt{3})$ and $(3, \lambda)$ from an equilateral triangle $AB = BC = CA$
$\Rightarrow AB ^2= BC ^2= CA ^2$
Now $,  AB ^2=\left( x _2- x _1\right)^2+\left( y _2- y _1\right)^2$
$=(3-0)^2+(\sqrt{3}-0)^2$
$=(3)^2+(\sqrt{3})^2$
$=9+3=12$
$BC ^2=(3-3)^2+(\lambda-\sqrt{3})^2$
$=(0)^2+(\lambda-\sqrt{3})^2=(\lambda-3)^2$
and $ CA ^2=(0-3)^2+(0-\lambda)^2$
$=(-3)^2+(-\lambda)^2$
$=9+\lambda^2$
$A B^2=C A^2 $
​​​​​​​$\Rightarrow 12=9+\lambda^2$
$\Rightarrow \lambda^2=12-9=3$
$\therefore \lambda= \pm \sqrt{3}$

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