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# The equation of the radical axis of the pair of circles $7x^2+7y^2-7x+14y+18=0$ and $4x^2+4y^2-7x+8y+20=0$ is :

$\begin {array} {1 1} (1)\;x-2y-5=0 & \quad (2)\;2x-y+5=0 \\ (3)\;21x - 68=0 & \quad (4)\;23x- 68=0 \end {array}$

(3) 21x-68=0