设甲投入X万元,则乙投入(3-X)万元,
Q=3/4[-(3-X)+3]=3/4X,
P+Q=3/4-1/4X^2+3/4X
=-1/4(X^2-3X-3)
=-1/4(X-3/2)^2+21/16,
∵-1/4