Let the latus ractum of the parabola

Question:

Let the latus ractum of the parabola $y^{2}=4 x$ be the common chord to the circles $C_{1}$ and $C_{2}$ each

of them having radius $2 \sqrt{5}$. Then, the distance

between the centres of the circles $\mathrm{C}_{1}$ and $\mathrm{C}_{2}$ is:

  1. 8

  2. $4 \sqrt{5}$

  3. 12

  4. $8 \sqrt{5}$


Correct Option: 1,

Solution:

Length of latus rectum $=4$

$\mathrm{DB}=2$

$C_{1} B=\sqrt{\left(C_{1} D\right)^{2}-(D B)^{2}}=4$

$\mathrm{C}_{1} \mathrm{C}_{2}=8$

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