组合(复合)图形的形心 由n个规则形状组成的图形A=∑A ∫ndA=∑∫d4=∑rA ∫al=al.∑ ∑y24 ∑=4 ∑4 ∑49 由 n 个规则形状组成的图形 y C z z y = = n i A Ai 1    = = = = = n i c i i n i Sz ydA yi dA y A 1 1 组合（复合）图形的形心   = = = = n i i n i ci i y c A z A A S z 1 1   = = = = n i i n i ci i z c A y A A S y 1 1    = = = = = n i c i i n i Sy zdA zi dA z A 1 1