(a+b)^2/2-2ab=(a²+2ab+b²)/2-2ab=(a²-2ab+b²)/2=(a-b)²/2≥0所以(a+b)²/2≥2aba^2+b^2-(a+b)^2/2=a²+b²-(a²+2ab+b²)/2=(a²-2ab+b²)/2=(a-b)²/2...