A) \[{{n}^{2}}({{l}^{2}}+{{m}^{2}})={{a}^{2}}\]
B) \[{{a}^{2}}({{l}^{2}}+{{m}^{2}})={{n}^{2}}\]
C) \[n(l+m)a\]
D) \[a(l+m)=n\]
Correct Answer: B
Solution :
Line \[y=mx+c\] is tangent, if\[c=\pm a\sqrt{1+{{m}^{2}}}\]. Now \[lx+my+n=0\] or \[y=-\frac{l}{m}x-\frac{n}{m}\] is tangent, if \[-\frac{n}{m}=\pm a\sqrt{1+{{\left( \frac{l}{m} \right)}^{2}}}\] or \[{{n}^{2}}={{a}^{2}}({{m}^{2}}+{{l}^{2}})\].
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