二次函数y=ax2+bx+c(a≠0)的性质可从二次函数的图像中由二次项系数a、判别式△、函数y三者之间的内在联系而得到: (1)若a>0且△=b2-4ac≤0.则y=ax2+bx+c≥0; (2)若a<0且△=b2-4ac≤0,则y=ax2+bx+c≤0. 应用上述性质(1)、(2)去证明一元二次不 The property of the quadratic function y=ax2+bx+c(a≠0) can be obtained from the quadratic function image by the intrinsic relationship between the quadratic coefficient a, the discriminant △, and the function y: (1 If a>0 and △=b2-4ac≤0, then y=ax2+bx+c≥0; (2) If a<0 and △=b2-4ac≤0, then y=ax2+bx+c≤ 0. Apply the above properties (1), (2) to prove that the one-arity quadratic does not