TR=P*Q=P*(12-2P),dTR/dP=?

TR=P*Q=P*(12-2P)=1/2*2P(12-2P)
≤1/2*[(2P+12-2P)/2]^2=18
(1)对正实数a,b,有a^2+b^2≥2ab (当且仅当a=b时取“=”号),a^2+b^2>0>-2ab
(2)对非负实数a,b,有a+b≥2√(a*b)≥0,即(a+b)/2≥√(a*b)≥0
(3)对负实数a,b,有a+