PreCal
posted by strate a stoodent on .
Classify the conic and write the equation in standard form:
(1) 9x^2 + 9y^2 + 18x  18y = 0
(2) 16x^2 + 16y^2  64x + 32y + 55 = 0
(3) 6x^2 + 2y^2 + 18x  10y + 2 = 0

the first two are circles, the last one is an ellipse
I will do the second one by
completing the square,
16x^2 + 16y^2  64x + 32y + 55 = 0
16(x^2  4x+ ___) + 16(y^2 + 2y + ___) = 55
16(x^2  4x+ 4) + 16(y^2 + 2y + 1) = 55+64+16
16(x^2  4x+ 4) + 16(y^2 + 2y + 1) = 25
(x2)^2 + (y+1)^2 = 25/16 
Oh, I see what I was doing wrong. I thought you had to SUBTRACT the numbers from the other side when you complete the square, but you have to ADD them. I get it now. Thanks!