已知直线y=-3/4x+3,它与x轴、y轴的交点分别为A、B两点,点C（m,n）是第二象限内一点,以点C为圆心的圆与x轴
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y = -3x/4 + 3
x = 0, y = 3, B(0, 3)
y = 0, x = 4, A(4, 0)
圆与x轴相切于点E, 半径为n, E(m, 0)
(1) 四边形OBCE是矩形, BC与x轴平行, C(m, 3), 半径为n = 3
C与直线y=-3/4x+3 (3x + 4y - 12 = 0)的距离为半径3 = |3m + 4*3-12|/√(9+16) = 3|m|/5
m = ±5, C是第二象限内一点, m = -5
C(-5, 3)
(2)
C(m, n)
-m = n = 半径
C与直线y=-3/4x+3 (3x + 4y - 12 = 0)的距离为半径:
n = |3m + 4n-12|/√(9+16) = |-3n + 4n -12|/5
= |n - 12|/5
n = 2, 或n = -3 (< 0, 舍去)
(3)
C(m, n), n = 半径
C与直线y=-3/4x+3 (3x + 4y - 12 = 0)的距离为半径:
n = |3m + 4n-12|/√(9+16) = |3m + 4n -12|/5
(a) n = (3m + 4n -12)/5
n = 3m - 12 < 0, 舍去
(b) n = -(3m + 4n -12)/5
n = (4-m)/3
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