1.3t=1.4,9t^2=1.96,v上=f(t)'=-1.96/4.8=-0.4083(m/s)
2.设离开x米 ,-x^2/√(25-x^2)=3,1/9*x^4+x^2-25=0,x1= -1/2*(-18+6*109^(1/2))^(1/2)
x2=1/2*(-18+6*109^(1/2))^(1/2),x1
1.3t=1.4,9t^2=1.96,v上=f(t)'=-1.96/4.8=-0.4083(m/s)
2.设离开x米 ,-x^2/√(25-x^2)=3,1/9*x^4+x^2-25=0,x1= -1/2*(-18+6*109^(1/2))^(1/2)
x2=1/2*(-18+6*109^(1/2))^(1/2),x1