Subject: conics - finding axis of symmetry
Who is asking: Student
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!
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 x2. Do the same for the terms involving y.
2(x2 - 4x) + 2(y2 + 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.