The distance of the point \((2,1,-1)\) from the plane \(x-2y+4z=9\) is
A. \(\frac{13}{21}\)
B. \(\frac{5}{\sqrt{21}}\)
C. \(\frac{13}{\sqrt{21}}\)
D. \(\frac{9}{\sqrt{21}}\)
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Best answer
Answer: C. \(\frac{13}{\sqrt{21}}\)
\(d=\frac{|2-2-4-9|}{\sqrt{1+4+16}}=\frac{13}{\sqrt{21}}\).
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· 23 Oct 2026
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