Medium
MCQ
+4 / -1
PYQ · JEE Mains 2025
Let $\mathrm{A}(x, y, z)$ be a point in $x y$-plane, which is equidistant from three points $(0,3,2),(2,0,3)$ and $(0,0,1)$.
Let $\mathrm{B}=(1,4,-1)$ and $\mathrm{C}=(2,0,-2)$. Then among the statements
(S1) : $\triangle \mathrm{ABC}$ is an isosceles right angled triangle, and
(S2) : the area of $\triangle \mathrm{ABC}$ is $\frac{9 \sqrt{2}}{2}$,
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A
both are false
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B
only (S2) is true
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C
only (S1) is true
Correct answer
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D
both are true
Solution
<p>$$\begin{aligned}
& A(x, y, z) \text { Let } P(0,3,2), Q(2,0,3), R(0,0,1) \\
& A P=A Q=A R \\
& x^2+(y-3)^2+(z-2)^2=(x-2)^2+y^2+(z-3)^2=x^2+ \\
& y^2+(z-1)^2
\end{aligned}$$</p>
<p>In xy plane $\mathrm{z}=0$</p>
<p>So, $x^2-4 x+4+y^2+9=x^2+y^2+1$</p>
<p>$$\begin{aligned}
& \Rightarrow y=2 \\
& x=3 \\
& 9+y^2-6 y+9+4=x^2+y^2+1
\end{aligned}$$</p>
<p>So, $A(3,2,0)$ also $B(1,4,-1) \& C(2,0,-2)$</p>
<p>Now $A B=\sqrt{4+4+1}=3$</p>
<p>$$\begin{aligned}
&\begin{aligned}
& \mathrm{AC}=\sqrt{1+4+4}=3 \\
& \mathrm{BC}=\sqrt{1+16+1}=\sqrt{18} \\
& \mathrm{AB}=\mathrm{AC} \\
& \text { isosceles } \Delta \& \mathrm{AB}^2+\mathrm{AC}^2=\mathrm{BC}^2 \\
& \text { right angle } \Delta \\
& \text { Area of } \triangle \mathrm{ABC}=\frac{1}{2} \times \text { base.height } \\
& \frac{1}{2} \times 3 \times 3=\frac{9}{2}
\end{aligned}\\
&\text { So only } S_1 \text { is true }
\end{aligned}$$</p>
About this question
Subject: Mathematics · Chapter: Three Dimensional Geometry · Topic: Direction Cosines and Ratios
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