因为
,
x=t2+2t y=2t3+3t2
所以
=2t+2,dx dt
=6t2+6t,dy dt
所以
=dy dx
=
dy dt
dx dt
,t+1 3t2+3t
所以
=
d2y dx2
(d dx
)=dy dx
(d dt
)dy dx
=dt dx
(d dt
)dy dx
1
dx dt
=
?3t2+3t?(6t+3)(t+1) (3t2+3t)2
1 6t2+6t
=
?3t2?6t?3 2×27(t2+1)3
=-
.(t+1)2
18(t2+1)3
故答案为:?
.(t+1)2
18(t2+1)3