Last Activity: 7 Years ago
Here we are given two lines a+ 2b and a which are inclined at 90 degrees.
Thus applying dot product on these lines,
a× (a+2b)=0
a^2+2ab=0
a^2=-2ab
a=-2b
Now a+b=r
-2b+b=r
Thus b+r=0. Or b=-r
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