2025 EJC Promo Q12

2025 EJC Promo Q12

Junior College 1
11 marks

Lines \(l_1\) and \(l_2\) have equations

respectively, where \(\lambda\) is a parameter and \(a, b\) are constants.

  1. It is given that lines \(l_1\) and \(l_2\) intersect each other at a right angle at point \(A\). Find the values of \(a\) and \(b\), and show that point \(A\) has coordinates \((4,1,3)\)[5]

Plane \(p_1\) has equation \(2x+z=-4\).

  1. Find the shortest distance from point \(A\) to plane \(p_1\).[2]

Plane \(p_2\) contains both lines \(l_1\) and \(l_2\), and has equation \(-11x+8y-5z=-51\).

  1. Find the acute angle between planes \(p_1\) and \(p_2\).[2]
  2. Hence, or otherwise, find the shortest distance of point \(A\) to line \(l_3\), the line of intersection between \(p_1\) and \(p_2\). (Give your answer to three significant figures.)[2]

Solution:

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Answer:(a) \(a=2\), \(b=1\), \(A=(4,1,3)\) (b) \(3\sqrt5\) (c) \(33.6^\circ\) (d) \(12.1\)

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