Question

若x＞y＞0,p=x^3+13xy^2与q=5x^2y 9y^3的大小关系是

Answer 1

p-q=x³+13xy²-5x²y-9y³=(x-y)(x²-4xy+9y²)

x＞y＞0,得 x-y＞0 x²-4xy+9y²=(x-2y)²+5y²＞0

∴ p＞q