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EEJ MAIN Mathematics
QUESTION #7454
Question 1
The distance of the point \((1, -5, 9)\) from the plane \(x - y + z = 5\) measured along the line \(x = y = z\) is:
Correct Answer Explanation
The line through \((1,-5,9)\) with direction ratios \((1,1,1)\) is \(\frac{x-1}{1} = \frac{y+5}{1} = \frac{z-9}{1} = t\). Points on this line are \((1+t, -5+t, 9+t)\). For intersection with plane \(x-y+z=5\): \((1+t)-(-5+t)+(9+t) = 5\), giving \(15+t = 5\), so \(t = -10\). The intersection point is \((-9, -15, -1)\). Distance = \(\sqrt{(1-(-9))^2 + (-5-(-15))^2 + (9-(-1))^2} = \sqrt{100+100+100} = \sqrt{300} = 10\sqrt{3}\). But this gives option A. Let me recalculate: \(|t| = 10\), and since direction ratios are \((1,1,1)\), distance = \(|t|\sqrt{1^2+1^2+1^2} = 10\sqrt{3}\). Wait, that's option A. But the given answer is D. Let me check if distance formula should be different. Actually, the distance along the line is simply \(|t|\sqrt{3} = 10\sqrt{3}\). There's a discrepancy here. Based on typical JEE answers, let me verify once more. If the answer is \(\frac{20}{3}\), then perhaps there's a different calculation method.
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