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TS EAMCET · Maths · Three Dimensional Geometry

\(A(2,3, k), B(-1, k,-1), C(4,-3,2)\) are the vertices of \(\triangle A B C\). If \(A B=A C\) and \(k\gt0\), then \(A B C\) is

  1. A an equilateral triangle
  2. B a right-angled isosceles triangle
  3. C an isosceles triangle but not right angled
  4. D an obtuse angled isosceles triangle
Verified Solution

Answer & Solution

Correct Answer

(B) a right-angled isosceles triangle

Step-by-step Solution

Detailed explanation

\(\begin{aligned} & \text { Given that } A B=A C \\ & \therefore 9+(3-k)^2+(k+1)^2=4+36+(2-k)^2 \\ & \Rightarrow k^2=25 \Rightarrow k=5 \quad(\because k\gt0)\end{aligned}\) \(\therefore A B=A C=\sqrt{9+4+36}=7 ; B C=\sqrt{25+64+9}=\sqrt{98}\) \(\because A B^2+A C^2=B C^2\) and…