1.設(shè)半徑為r,則高為3r.
2*3.14*r^2+2*3.14*r*（3r)=628
6.28r^2+18.84r^2=628
25.12r^2=628
r^2=25
r=5
高 3r=3*5=15(cm)
這個圓柱的側(cè)面積是:2*3.14*5*15=471(cm^2)
2.2 ∏rh=100
∏rh=50
又 ∏r^2h=250
(∏rh)r=250
50r=250
r=5
3 r1/r2=1/3 h1/h2=8/9
v1:v2=(1/3∏r1^2h1):(1/3∏r2^2h2)
=(r1/r2)^2*(h1/h2)
=1/3*1/3*8/9
=8/81
=8:81
4 1250*(15-12)
=1250*3
=3750(cm^3)