若直线AX+BY-3=0与圆X^2+Y^2+4X-1=0切于点P(-1,2),则A*B的值为
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圆X^2+Y^2+4X-1=0 == (x+2)^2 +y^2 = 5 圆心O(-2,0), 直线OP斜率=2直线L过点P(-1,2), 斜率=-1/直线OP斜率 = -1/2== 直线L方程: y-2 = (-1/2)(x+1) == x+2y-3=0== A = 1, B = 2== A*B = 2
若直线AX+BY-3=0与圆X^2+Y^2+4X-1=0切于点P(-1,2),则A*B的值为
圆X^2+Y^2+4X-1=0 == (x+2)^2 +y^2 = 5 圆心O(-2,0), 直线OP斜率=2直线L过点P(-1,2), 斜率=-1/直线OP斜率 = -1/2== 直线L方程: y-2 = (-1/2)(x+1) == x+2y-3=0== A = 1, B = 2== A*B = 2