因为:σ^2=EX^2-(EX)^2所以:EX^2=σ^2+(EX)^2则:E(7-4X+2X^2)=E(7)+E(-4X)+E(2X^2)=7-4E(X)+2E(X^2)=7-4*1.5+2*(0.8*0.8+1.5*1.5)=3.89此题关键是要知道公式:σ^2=EX^2-(EX)^2