a
LI² + RI + 1/C = 0 for I
I^2+RI/L+1/CL=0(L≠0）
(I+R/2L)^2+1/CL-R^2/4L^2=0
(I+R/2L)^2=R^2/4L^2-1/CL
I = [-RC ± √(R^2*C^2 - 4LC)]/2LC
b
(x-k)² + (y-k)² = r² for y
(y-k)^2=r^2-(x-h)^2
y = k ± √[r^2 - (x - h)^2]