x^2-xy+ y^2=1
2x- ( xy' + y) +2y.y' =0
(x-2y)y' = 2x-y
y' = (2x-y)/(x-2y)
y''
= [(x-2y)(2-y') - (2x-y)(1-2y') ]/(x-2y)^2
= [(x-2y)( 2-(2x-y)/(x-2y) ) - (2x-y)( 1-2(2x-y)/(x-2y) ) ]/(x-2y)^2
= [(x-2y)( 2(x-2y)-(2x-y) ) - (2x-y)( (x-2y)-2(2x-y) ) ]/(x-2y)^3
= [(x-2y)( -3y ) - (2x-y)( -3x ) ]/(x-2y)^3
=-3( xy-6y^2 - 2x^2+xy) /(x-2y)^3
=6( x^2-xy+3y^2 ) /(x-2y)^3
内容全部来源于网络收集，如有侵权，请联系网站删除：QQ：24596024