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问题: 一道数学题

设三棱柱ABC-A1B1C1的体积为V,P为其侧棱BB1上的任意一点,则四棱锥P-ACC1A1的体积为___

答案:2V/3

详细过程,谢谢~

解答:

设三棱柱ABC-A1B1C1的体积为V,P为其侧棱BB1上的任意一点,则四棱锥P-ACC1A1的体积为

V = V(ABC-A1B1C1)
 = V(P-ABC) + V(P-A1B1C1) + V(P-ACC1A1)
 = (1/3)S底*PB + (1/3)S底*PB1 + V(P-ACC1A1)
 = (1/3)S底*(PB+PB1) + V(P-ACC1A1)
 = (1/3)S底*高 + V(P-ACC1A1)
 = (1/3)V + V(P-ACC1A1)
--->V(P-ACC1A1) = 2V/3