The angle between the pair of straight lines formed by joining the points of intersection of `x^2+y^2=4` and `y=3x+c` to the origin is a right angle. Then `c^2` is equal to

Options

A. 20
B. 13
C. `1//5`
D. 5

Answer

A

Explanation

Now , homogenising the given curve , we get `x^2+y^2=4((y-3x)/(c))^2`
`rArr c^2(x^2+y^2)=4(y^2+9x^2-6xy)`
Since , lines are at right angle.
`therefore` Coefficient of `x^2+` Coefficient of `y^2=0`
`rArr c^2-36+c^2-4=0rArr c^2=20` .