a=2+6x^2
dv/dx*dx/dt=2+6x^2
vdv=(2+6x^2)dx
∫vdv=∫(2+6x^2)dx
v^2=4x+4x^3+c (1)式
x=0,v=10代入得c=100
(1)式开方得
v=2根号x+x^3+25