Bt tham khảo gt2 nhóm 2

SKM 368e20030315140 Admin Typewriter y f''''(x^2 y^2)x =y (x^2 y^2)''''x f''''(x^2 y^2 =y 2x f'''' Admin Typewriter y f''''(x^2 y^2)y+f(x^2 y^2) = 2y^2 f''''+f Admin Typewriter 1/x y 2x f'''' + 1/y ( 2y^2 f+f) =2yf'''' 2yf''''+[.]

y f'(x^2-y^2)x

=y (x^2-y^2)'x .f'(x^2-y^2

=y.2x f'

y.f'(x^2-y^2)y+f(x^2-y^2)

=-2y^2.f'+f

1/x.y.2x.f' + 1/y (-2y^2.f+f)

=2yf'-2yf'+1/y f

=y.f/y^2=z/y^2 (dpcm)