L1 is a line intersecting x and y axes at A(a,0) and B(0,b).L2 is a line perpendicular to L1 intersecting x and y axes at C and D respectiveley. If the area of the triangle OCD is 4 times the area of triangle OAB, then equation of AD is
A
x+2y=26
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B
2x+y+2a=0
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C
x−2y+2b=0
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D
2x−y−2a=0
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Solution
The correct option is D2x−y−2a=0 Equation of AB:xa+yb=1 L2⊥L1⇒xb−ya=α ⇒xαb+y−αa=1 C:(αb,0),D:(0,−αa) Ar(ΔOCD) =∣∣∣12×OC×OD∣∣∣=∣∣∣12×(αb)(−αa)∣∣∣=α22|ab|
Ar(ΔOAB) =∣∣∣12×OA×OB∣∣∣=12|ab| ⇒α22|ab|=4×12|ab|⇒α=±2 A(a,0),D(0,∓2a)
Line passing through A and D ⇒xa+y∓2a=1⇒2x∓y−2a=0