圆台下底面半径r1=r*ctn15°,上底面半径r2=r*ctn75°.高显然是2rr1+r2=r(ctn15°+ctn75°)=4r(r1-r2)²=r²(ctn15°-ctn75°)²=12r²r1²+r1*r2+r2²=(r1-r2)²+3r1*r2=12r²+3r&#...