10-1.Circle and System of Circles
hard

यदि वक्र $x ^{2}-6 x + y ^{2}+8=0$ तथा $x ^{2}-8 y + y ^{2}+$ $16- k =0,( k >0)$ एक दूसरे को एक बिन्दू पर स्पर्श करते हैं, तो $k$ का अधिकतम मान है

A

$25$

B

$36$

C

$30$

D

$42$

(JEE MAIN-2020)

Solution

Common tangent is $\mathrm{S}_{1}-\mathrm{S}_{2}=0$

$\Rightarrow-6 x+8 y-8+k=0$

Use $\mathrm{p}=\mathrm{r}$ for $\mathrm{I}^{\text {st }}$ circle

$\Rightarrow \frac{|-18-8+k|}{10}=1$

$\Rightarrow \mathrm{k}=36$ or $16 \Rightarrow \mathrm{k}_{\max }=36$

Standard 11
Mathematics

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