f(x,y,z,p,q)=p2+q2−2px−2qy+1=0
Charpit's auxiliary equation are:
fx+pfzdp=fy+qfzdq=−pfp−qfqdz=−fpdx=−fqdy
or
pdp=qdq=p(p−x)+q(q−y)dz=p−xdx=q−ydy
Taking first two fractions,
pdp=qdq
Integrating, lnp=lnq+lnaorp=aq.
Putting p=aq into f(x, y, z, p, q), we get:
a2q2+q2−2aqx−2qy+1=0q2(a2+1)−2q(ax+y)+1=0
Solve for q
q=2(a2+1)2(ax+y)±4(ax+y)2−4(a2+1)
Let's (ax+y)=u and (a2+1)=b= const
q=bu±u2−b
p=aq=ba(u±u2−b)
We know that
dz=pdx+qdy=aqdx+qdy=q(adx+dy)=qd(ax+y)=qdu
Integrating
z=∫bu±u2−bdu=2bu2±b1∫u2−bdu=
=2bu2±21uu2−b−21bln(u2−b+u)+C==2b(ax+y)2±21(ax+y)(ax+y)2−b−21bln((ax+y)2−b+(ax+y))+C
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