Subject: conics  finding axis of symmetry Name: Quinn Who is asking: Student Level: Secondary
Question:
2x^{2}+2y^{2}8x+12y+16=0
x^{2}+2y^{2}2x+8y4=0 I think this one is a parabola and the book says if A=0 y==E/2C; if C=0 x=D/2A. Well ok but how do you find x when A=0 or y when C=0?? Help!! None of this is makes any sense! Hi Quinn, I would approach these problems another way, without using the standard form. For the first problem,
collect the terms involving x together and factor from these terms the coefficient of x^{2}. Do the same for the terms involving y.
2(x^{2}  4x) + 2(y^{2} + 6y) + 16 = 0 Now complete the square for both the x and y terms, adding the appropriate values to the right side to maintain the equality
The expression then becomes
(x  2)^{2} + (y + 3)^{2} = 5
In this form the conic is recognizable as the circle with center (2,3) and radius the square root of 5.
Cheers,
