BITSAT 2013 Paper

Equation of pair of tangents is given by
SS1 = T2
or S = x2+y2 + 20 (x + y) + 20 , S1 = 20 ,
T = 10 (x + y) + 20 = 0
∴ SS1 = T2
⇒ 20 (x2+y2 + 20 (x + y) + 20) = 102 (x+y+2)2
⇒ 4x2+4y2 + 10xy 0 ⇒ 2x2+2y2 + 5xy = 0