(2012•台湾)判断下列哪一组的a、b、c,可使二次函数y=ax2+bx+c-5x2-3x+7在坐标平面上的图形有最低点?( )A.a=0,b=4,c=8 B.a=2,b=4,c=-8 C.a=4,b=-4,c=8 D.a=6,b=-4,c=-8
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![(2012•台湾)判断下列哪一组的a、b、c,可使二次函数y=ax2+bx+c-5x2-3x+7在坐标平面上的图形有最低点?( )A.a=0,b=4,c=8 B.a=2,b=4,c=-8 C.a=4,b=-4,c=8 D.a=6,b=-4,c=-8](/uploads/image/z/766120-40-0.jpg?t=%EF%BC%882012%26%238226%3B%E5%8F%B0%E6%B9%BE%EF%BC%89%E5%88%A4%E6%96%AD%E4%B8%8B%E5%88%97%E5%93%AA%E4%B8%80%E7%BB%84%E7%9A%84a%E3%80%81b%E3%80%81c%2C%E5%8F%AF%E4%BD%BF%E4%BA%8C%E6%AC%A1%E5%87%BD%E6%95%B0y%3Dax2%2Bbx%2Bc-5x2-3x%2B7%E5%9C%A8%E5%9D%90%E6%A0%87%E5%B9%B3%E9%9D%A2%E4%B8%8A%E7%9A%84%E5%9B%BE%E5%BD%A2%E6%9C%89%E6%9C%80%E4%BD%8E%E7%82%B9%3F%EF%BC%88%E3%80%80%E3%80%80%EF%BC%89A%EF%BC%8Ea%3D0%2Cb%3D4%2Cc%3D8+B%EF%BC%8Ea%3D2%2Cb%3D4%2Cc%3D-8+C%EF%BC%8Ea%3D4%2Cb%3D-4%2Cc%3D8+D%EF%BC%8Ea%3D6%2Cb%3D-4%2Cc%3D-8)
(2012•台湾)判断下列哪一组的a、b、c,可使二次函数y=ax2+bx+c-5x2-3x+7在坐标平面上的图形有最低点?( )A.a=0,b=4,c=8 B.a=2,b=4,c=-8 C.a=4,b=-4,c=8 D.a=6,b=-4,c=-8
(2012•台湾)判断下列哪一组的a、b、c,可使二次函数y=ax2+bx+c-5x2-3x+7在坐标平面上的图形有最低点?( )
A.a=0,b=4,c=8 B.a=2,b=4,c=-8
C.a=4,b=-4,c=8 D.a=6,b=-4,c=-8
(2012•台湾)判断下列哪一组的a、b、c,可使二次函数y=ax2+bx+c-5x2-3x+7在坐标平面上的图形有最低点?( )A.a=0,b=4,c=8 B.a=2,b=4,c=-8 C.a=4,b=-4,c=8 D.a=6,b=-4,c=-8
y=ax2+bx+c-5x2-3x+7=(a-5)x2+(b-3)x+(c+7),
若使此二次函数图形有最低点,则图形的开口向上,即x2项系数为正数,
∴a-5>0,
∴a>5,
故选D.