Question

Write the equation of a parabola whose directrix is

y

=

−

1.5

y

=

-

1.5

and has a focus at

(

−

4

,

−

2.5

)

(

-

4

,

-

2.5

)

.

Answer 1

y=0.5x²-4x-10.

Explanation:

1) according to the definition of parabola:

d1=d2, then

`2) \ |y+1.5|=√((x+4)^2+(y+2.5)^2) ;`

3) after evolution:

-(2y+4)=(x+4)²; ⇔

`y=-(1)/(2)x^2-4x-10.`