由P=F/S F=G=ρgL^3 S=L^2 P=ρLgP1=ρa1^3g/a1^2=ρa1g.P2=ρa2^3g/a2^2=ρa2g.把甲放在乙的上面,则乙对桌面的压强为P=(ρa1^3g+ρa2^3g)/a2^2=ρa1^3g/a2^2+P2=(P1^3+P2^3)/P2^2
