1.

Two parabola have the same focus. If their directrices are the x-axis and the y-axis respectively, then the slope of their common chord is :

Answer» F(n,k)
D_1:y=0
D_2:x=0
`P_1:(x-h)^2+(y-k)^2=y^2`
`sqrt((x-h)^2+(y-k)^2)=|(lx+my+n)/sqrt(l^2+m^2)|`
`x^2-2hx+h^2+y^2-2yk+k^2=y^2`
`P_1:x^2-2hx-2yk+h^2+k^2=0-(1)`
`P_2:x^2-2hx+h^2+y^2-2yk+k^2=x^2`
`y^2-2hx-2yk+h^2+k^2=0`
Chord=`P_1=P_2`
`x^2-2hx-2yk+h^2+k^2-y^2+2hx+2ykh^2-k^2=0`
`y^2-x^2=0`
`(y-x)(y+x)=0`
`m=1,-1`
option 1 is correct.


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