A) -16
B) 9
C) 16
D) 25
Correct Answer: A
Solution :
Circles x2 + y2 = 4, x2 + y2 ? 10x + l = 0 touch externally \ \[{{C}_{1}}{{C}_{2}}={{r}_{1}}+{{r}_{2}}\] Þ \[{{C}_{1}}(0,\,0)\] and \[{{C}_{2}}=(5,\,0)\] \[{{r}_{1}}=2\] and \[{{r}_{2}}=\sqrt{25+\lambda }\] \ \[\sqrt{{{(5-0)}^{2}}+0}=2+\sqrt{25+\lambda }\] Þ \[5-2=\sqrt{25+\lambda }\] Þ \[3=\sqrt{25+\lambda }\] Þ \[9=25+\lambda \] Þ l = ? 16.
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