BANG CACH DA.T Y= 1Z R^OI DA.T Z =UX,HA~Y GIA'IPHU.O.NG TRNH
16)
Bang cach da.t
y= 1zr^oi da.t
z =ux,ha~y gia'i
phu.o.ng trnh:
(x2
y2
−1)dy+ 2xy3
dx= 0HD gia’i:D - a.t
y = 1zdu.o..c:
(z2
−x2
)dz + 2zxdx = 0; r^oi da.t
z = ux, du.o..c
(u2
−1)(udx+xdu) + 2udx= 0⇐⇒ dxx + u2
−1u3
+udu= 0⇐⇒ ln|x|+ lnu2
+ 1|u| = lnC ⇐⇒ x(u2
+ 1)u =Cthay
u= 1xydu.o..c nghi^e.m
1 +x2
y2
=Cy