1.

The focal distance of a point of a parabola `y^(2)=8x` is 5. Find the abscissa of that point.

Answer» `y^(2)=8x`
Comparing with `y^(2)=ax`
4a=8
`rArr" "a=2`
Equation of directrix
x=-a
`rArr" "x=-2`
`rArr" "x+2=0`
Let `(x_(1),y_(1))` be any point on the parabola and its focal distance is 5.
`:.` Distance of point `(x_(1),y_(1))` from directrix = distance of point `(x_(1),y_(1))` from focus
`rArr" "x_(1)+2=5`
`rArr" "x_(1)=3`
`:.` Abscissa of required point = 3.


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