# A pair of perpendicular lines passes through the origin and also through the points of intersection of the curve $x^2+y^2 =4$ with $x+y=a,$ where $a > 0$. Then $a=$

$\begin {array} {1 1} (1)\;2 & \quad (2)\;3 \\ (3)\;4 & \quad (4)\;5 \end {array}$

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answered Nov 7, 2013 by

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