10-1.Circle and System of Circles
hard

જો ચલિત રેખા $3 x+4 y=\alpha$ એ બે વર્તુળો $(x-1)^{2}+(y-1)^{2}=1$ અને $(x-9)^{2}+(y-1)^{2}=4$ ની વચ્ચે એવી રીતે આવેલ છે કે જેથી તે બંને વર્તુળની એકપણ જીવાને છેદતી નથી તો $\alpha$ ની બધીજ પૃણાંક કિમંતોનો સરવાળો મેળવો.

A

$164$

B

$166$

C

$165$

D

$199$

(JEE MAIN-2021)

Solution

Both centres should lie on either side of the line as well as line can be tangent to circle.

$(3+4-\alpha) \cdot(27+4-\alpha)\,<\,0$

$(7-\alpha) \cdot(31-\alpha)<0 \Rightarrow \alpha \in(7,31) \quad \ldots(1)$

$d_{1}=\text { distance of }(1,1) \text { from line }$

$d_{2}=\text { distance of }(9,1) \text { from line }$

$d_{1} \geq r_{1} \Rightarrow \frac{|7-\alpha|}{5} 1 \Rightarrow \alpha \in(-\infty, 2] \cup[12, \infty) \ldots(2)$

$d_{2} \geq r_{2} \Rightarrow \frac{|31-\alpha|}{5} \geq 2 \Rightarrow \alpha \in(-\infty, 21] \cup[41, \infty)\ldots(3)$

$(1) \cap(2) \cap(3) \Rightarrow \alpha \in[12,21]$

Sum of integers $=165$

Standard 11
Mathematics

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