JEE Advance - Mathematics (2024 - Paper 2 Online - No. 7)

Let $A_1, B_1, C_1$ be three points in the $x y$-plane. Suppose that the lines $A_1 C_1$ and $B_1 C_1$ are tangents to the curve $y^2=8 x$ at $A_1$ and $B_1$, respectively. If $O=(0,0)$ and $C_1=(-4,0)$, then which of the following statements is (are) TRUE?
The length of the line segment $O A_1$ is $4 \sqrt{3}$
The length of the line segment $A_1 B_1$ is 16
The orthocenter of the triangle $A_1 B_1 C_1$ is $(0,0)$
The orthocenter of the triangle $A_1 B_1 C_1$ is $(1,0)$

Explanation

JEE Advanced 2024 Paper 2 Online Mathematics - Parabola Question 2 English Explanation

Equation of tangent at (2t$$^2$$, 4t) is

$$\mathrm{ty}=\mathrm{x}+2 \mathrm{t}^2$$

$$\because$$ It is passing through $$(-4,0)$$

$$\therefore 0=-4+2 \mathrm{t}^2 \Rightarrow \mathrm{t}= \pm \sqrt{2}$$

$$\left.\begin{array}{rl} \therefore & \mathrm{A}_1=(4,4 \sqrt{2}) \\ & \mathrm{B}_1=(4,-4 \sqrt{2}) \end{array}\right\} \quad \begin{aligned} & \mathrm{OA}_1=\sqrt{48}=4 \sqrt{3} \\ & \mathrm{~A}_1 \mathrm{~B}_1=8 \sqrt{2} \end{aligned}$$

Equation of altitude of $$\Delta A_1 B_1 C_1$$ drawn from $$A_1$$ is

$$\begin{aligned} & y-4 \sqrt{2}=\sqrt{2}(x-4) \\ & \Rightarrow \sqrt{2} x-y=0 \quad \text{... (1)} \end{aligned}$$

Equation of altitude of $$\Delta A_1 B_1 C_1$$ drawn from $$C_1$$ is

$$\mathrm{x}=0\quad \text{... (2)}$$

Solving (1) and (2) $$\Rightarrow$$ orthocentre is $$(0,0)$$

$$\therefore$$ correct options are (A), (C)

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