推 XII :=> (a_1t^2+a_2)(b_1t+b_2)≧0 for all t＞0 08/28 19:22
Find the necessary and sufficient conditions of a_1,a_2,b_1, and b_2
with a_1>0,a_2<0,b_1>0, and b_2<0 such that
a_1*b_1*x^3+a_1*b_2*x^2*y+a_2*b_1*x*y^2+a_2*b_2*y^3\geq 0 for all x,y>0
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