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3x2y-4xy2; x2y-4xy2; x2y+2xy2; -x2y-2xy2
y=x-2 y=x+2 y=2x+1 y=-2x+1
y=-2x+4 y=x+4 y=-2x- y=x-
xy(2x-2y)2 2xy(x-y)2 4xy(x2-2xy+y2) 4xy(x-y)2
x2 –2xy+y2=x(x-2y)+y2 x2-16y2=(x+8y)(x-8y)
x2+xy+y2=(x+y)2 x4y4-1=(x2y2+1)(xy+1)(xy-1)
, 两点,若|AB|=10,则AB的中点到y轴的距离等于( ) A.1B.2 3 4
(1,2)且垂直于直线2x+y﹣5=0的直线方程为( ) A.x﹣2y+4=0 2x+y﹣7=0 x﹣2y+3=0 x﹣2y+5=0
(2,3)且垂直于直线2x+y-5=0的直线方程为( ). A.x-2y+4=0 2x+y-7=0 x-2y+3=0 x-2y+5=0
(x1,y1), (x2,y2)两点,如果x1+x2=6,那么|AB|等于 ( ). A.10B.8 6 4
x-2y-2=0 x-2y+2=0 x+2y-2=0 x+2y+2=0
-x2-y2 = -(x+y)(x-y) x2y+2xy+4y = y(x+2)2 -49x2+x2y2 = (xy+7x)(xy-7x) 16x2+4y2-16xy = 4(2x-y)2