Thread: Conics!!!

Hi, I need some help with this math problem:


Given the general form of a conic 2x^2+C y^2 +8x -y +F = 0 .
What would be the values of C and F that make the conic a parabola opening upward with
its vertex at (-2,1) ? Given the equation of this conic.

Please someone help me!.

Originally Posted by Kal

Hi, I need some help with this math problem:


Given the general form of a conic 2x^2+C y^2 +8x -y +F = 0 .
What would be the values of C and F that make the conic a parabola opening upward with
its vertex at (-2,1) ? Given the equation of this conic.

Please someone help me!.

It should be clear that C = 0.

Then y = 2x^2 + 8x + F = 2(x^2 + 4x + F/2) = 2([x + 2]^2 - 4 + F/2) = 2[x + 2]^2 - 8 + F.

Threfore - 8 + F = 1 (why?). Therefore F = 9.

awesome!!! thanks a lot!